Cannot install from sourcedist

This appears to fail with flit (even if flit is installed)

Disabling build isolation with --no-build-isolation appears to be fixing it if flit is already installed in the environment.

cc @takluyver

```
>>> pip install ipykernel --no-binary :all:
Collecting ipykernel
Using cached https://files.pythonhosted.org/packages/b1/4e/288d4f30d1f121809a0f0df78373ef8b2d9eea9d7eb879cddb0b074af4d1/ipykernel-5.1.3.tar.gz
Installing build dependencies ... error
ERROR: Complete output from command /home/sylvain/miniconda3/bin/python /home/sylvain/miniconda3/lib/python3.7/site-packages/pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-k0hs5oyp/overlay --no-warn-script-location --no-binary :all: --only-binary :none: -i https://pypi.org/simple -- setuptools wheel 'ipython>=5' 'jupyter_core>=4.2' jupyter_client:
ERROR: Collecting setuptools
Using cached https://files.pythonhosted.org/packages/f4/d5/a6c19dcbcbc267aca376558797f036d9bcdff344c9f785fe7d0fe9a5f2a7/setuptools-41.4.0.zip
Collecting wheel
Using cached https://files.pythonhosted.org/packages/59/b0/11710a598e1e148fb7cbf9220fd2a0b82c98e94efbdecb299cb25e7f0b39/wheel-0.33.6.tar.gz
Collecting ipython>=5
Using cached https://files.pythonhosted.org/packages/89/60/acb98588d8eba96558e69d90fa54f9908b4e48f6492ff378697f0c2216e2/ipython-7.8.0.tar.gz
Collecting jupyter_core>=4.2
Using cached https://files.pythonhosted.org/packages/a4/47/e852cd00ae811939201b7f8118a856f2c6a52db3b31c4185ffbc098405c7/jupyter_core-4.6.0.tar.gz
Collecting jupyter_client
Using cached https://files.pythonhosted.org/packages/c4/cf/ccd7bc6935b60fe4470d7c209e4edde5e18058938f6e81aa0e9db5578c54/jupyter_client-5.3.4.tar.gz
Collecting jedi>=0.10 (from ipython>=5)
Using cached https://files.pythonhosted.org/packages/85/03/cd5a6e44a5753b4d539288d9d1f9645caac889c17dd2950292a8818f86b2/jedi-0.15.1.tar.gz
Collecting decorator (from ipython>=5)
Using cached https://files.pythonhosted.org/packages/ba/19/1119fe7b1e49b9c8a9f154c930060f37074ea2e8f9f6558efc2eeaa417a2/decorator-4.4.0.tar.gz
Collecting pickleshare (from ipython>=5)
Using cached https://files.pythonhosted.org/packages/d8/b6/df3c1c9b616e9c0edbc4fbab6ddd09df9535849c64ba51fcb6531c32d4d8/pickleshare-0.7.5.tar.gz
Collecting traitlets>=4.2 (from ipython>=5)
Using cached https://files.pythonhosted.org/packages/75/b0/43deb021bc943f18f07cbe3dac1d681626a48997b7ffa1e7fb14ef922b21/traitlets-4.3.3.tar.gz
Collecting prompt_toolkit<2.1.0,>=2.0.0 (from ipython>=5)
Using cached https://files.pythonhosted.org/packages/0c/37/7ad3bf3c6dbe96facf9927ddf066fdafa0f86766237cff32c3c7355d3b7c/prompt_toolkit-2.0.10.tar.gz
Collecting pygments (from ipython>=5)
Using cached https://files.pythonhosted.org/packages/7e/ae/26808275fc76bf2832deb10d3a3ed3107bc4de01b85dcccbe525f2cd6d1e/Pygments-2.4.2.tar.gz
Collecting backcall (from ipython>=5)
Using cached https://files.pythonhosted.org/packages/84/71/c8ca4f5bb1e08401b916c68003acf0a0655df935d74d93bf3f3364b310e0/backcall-0.1.0.tar.gz
Collecting pexpect (from ipython>=5)
Using cached https://files.pythonhosted.org/packages/1c/b1/362a0d4235496cb42c33d1d8732b5e2c607b0129ad5fdd76f5a583b9fcb3/pexpect-4.7.0.tar.gz
Collecting pyzmq>=13 (from jupyter_client)
Using cached https://files.pythonhosted.org/packages/7a/d2/1eb3a994374802b352d4911f3317313a5b4ea786bc830cc5e343dad9b06d/pyzmq-18.1.0.tar.gz
Collecting python-dateutil>=2.1 (from jupyter_client)
Using cached https://files.pythonhosted.org/packages/ad/99/5b2e99737edeb28c71bcbec5b5dda19d0d9ef3ca3e92e3e925e7c0bb364c/python-dateutil-2.8.0.tar.gz
Installing build dependencies: started
Installing build dependencies: finished with status 'done'
Getting requirements to build wheel: started
Getting requirements to build wheel: finished with status 'done'
Preparing wheel metadata: started
Preparing wheel metadata: finished with status 'done'
Collecting tornado>=4.1 (from jupyter_client)
Using cached https://files.pythonhosted.org/packages/30/78/2d2823598496127b21423baffaa186b668f73cd91887fcef78b6eade136b/tornado-6.0.3.tar.gz
Collecting parso>=0.5.0 (from jedi>=0.10->ipython>=5)
Using cached https://files.pythonhosted.org/packages/21/40/615957db4d178b7504c87b1a5b85fa5945b0b4fa5f5a845e31fc7aad6018/parso-0.5.1.tar.gz
Collecting ipython_genutils (from traitlets>=4.2->ipython>=5)
Using cached https://files.pythonhosted.org/packages/e8/69/fbeffffc05236398ebfcfb512b6d2511c622871dca1746361006da310399/ipython_genutils-0.2.0.tar.gz
Collecting six (from traitlets>=4.2->ipython>=5)
Using cached https://files.pythonhosted.org/packages/dd/bf/4138e7bfb757de47d1f4b6994648ec67a51efe58fa907c1e11e350cddfca/six-1.12.0.tar.gz
Collecting wcwidth (from prompt_toolkit<2.1.0,>=2.0.0->ipython>=5)
Using cached https://files.pythonhosted.org/packages/55/11/e4a2bb08bb450fdbd42cc709dd40de4ed2c472cf0ccb9e64af22279c5495/wcwidth-0.1.7.tar.gz
Collecting ptyprocess>=0.5 (from pexpect->ipython>=5)
Using cached https://files.pythonhosted.org/packages/7d/2d/e4b8733cf79b7309d84c9081a4ab558c89d8c89da5961bf4ddb050ca1ce0/ptyprocess-0.6.0.tar.gz
Installing build dependencies: started
Installing build dependencies: still running...
Installing build dependencies: finished with status 'error'
ERROR: Complete output from command /home/sylvain/miniconda3/bin/python /home/sylvain/miniconda3/lib/python3.7/site-packages/pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-2yzid3qp/overlay --no-warn-script-location --no-binary :all: --only-binary :none: -i https://pypi.org/simple -- flit:
ERROR: Collecting flit
Using cached https://files.pythonhosted.org/packages/1f/87/9ea76ab4cdf1fd36710d9688ec36a0053067c47e753b32272f952ff206c5/flit-1.3.tar.gz
Installing build dependencies: started
Installing build dependencies: finished with status 'done'
Getting requirements to build wheel: started
Getting requirements to build wheel: finished with status 'done'
Installing backend dependencies: started
Installing backend dependencies: finished with status 'done'
Preparing wheel metadata: started
Preparing wheel metadata: finished with status 'done'
Collecting docutils (from flit)
Using cached https://files.pythonhosted.org/packages/93/22/953e071b589b0b1fee420ab06a0d15e5aa0c7470eb9966d60393ce58ad61/docutils-0.15.2.tar.gz
Collecting pytoml (from flit)
Using cached https://files.pythonhosted.org/packages/f4/ba/98ee2054a2d7b8bebd367d442e089489250b6dc2aee558b000e961467212/pytoml-0.1.21.tar.gz
Collecting requests (from flit)
Using cached https://files.pythonhosted.org/packages/01/62/ddcf76d1d19885e8579acb1b1df26a852b03472c0e46d2b959a714c90608/requests-2.22.0.tar.gz
Collecting chardet<3.1.0,>=3.0.2 (from requests->flit)
Using cached https://files.pythonhosted.org/packages/fc/bb/a5768c230f9ddb03acc9ef3f0d4a3cf93462473795d18e9535498c8f929d/chardet-3.0.4.tar.gz
Collecting idna<2.9,>=2.5 (from requests->flit)
Using cached https://files.pythonhosted.org/packages/ad/13/eb56951b6f7950cadb579ca166e448ba77f9d24efc03edd7e55fa57d04b7/idna-2.8.tar.gz
Collecting urllib3!=1.25.0,!=1.25.1,<1.26,>=1.21.1 (from requests->flit)
Using cached https://files.pythonhosted.org/packages/ff/44/29655168da441dff66de03952880c6e2d17b252836ff1aa4421fba556424/urllib3-1.25.6.tar.gz
Collecting certifi>=2017.4.17 (from requests->flit)
Using cached https://files.pythonhosted.org/packages/62/85/7585750fd65599e88df0fed59c74f5075d4ea2fe611deceb95dd1c2fb25b/certifi-2019.9.11.tar.gz
Skipping bdist_wheel for flit, due to binaries being disabled for it.
Skipping bdist_wheel for docutils, due to binaries being disabled for it.
Skipping bdist_wheel for pytoml, due to binaries being disabled for it.
Skipping bdist_wheel for requests, due to binaries being disabled for it.
Skipping bdist_wheel for chardet, due to binaries being disabled for it.
Skipping bdist_wheel for idna, due to binaries being disabled for it.
Skipping bdist_wheel for urllib3, due to binaries being disabled for it.
Skipping bdist_wheel for certifi, due to binaries being disabled for it.
Installing collected packages: docutils, pytoml, chardet, idna, urllib3, certifi, requests, flit
Running setup.py install for docutils: started
Running setup.py install for docutils: finished with status 'done'
Running setup.py install for pytoml: started
Running setup.py install for pytoml: finished with status 'done'
Running setup.py install for chardet: started
Running setup.py install for chardet: finished with status 'done'
Running setup.py install for idna: started
Running setup.py install for idna: finished with status 'done'
Running setup.py install for urllib3: started
Running setup.py install for urllib3: finished with status 'done'
Running setup.py install for certifi: started
Running setup.py install for certifi: finished with status 'done'
Running setup.py install for requests: started
Running setup.py install for requests: finished with status 'done'
Running setup.py install for flit: started
Running setup.py install for flit: finished with status 'error'
ERROR: Complete output from command /home/sylvain/miniconda3/bin/python -u -c 'import setuptools, tokenize;__file__='"'"'/tmp/pip-install-3u8xm43a/flit/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record /tmp/pip-record-dn9u9vvj/install-record.txt --single-version-externally-managed --prefix /tmp/pip-build-env-2yzid3qp/overlay --compile:
ERROR: Traceback (most recent call last):
File "", line 1, in
ModuleNotFoundError: No module named 'setuptools'
----------------------------------------
ERROR: Command "/home/sylvain/miniconda3/bin/python -u -c 'import setuptools, tokenize;__file__='"'"'/tmp/pip-install-3u8xm43a/flit/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record /tmp/pip-record-dn9u9vvj/install-record.txt --single-version-externally-managed --prefix /tmp/pip-build-env-2yzid3qp/overlay --compile" failed with error code 1 in /tmp/pip-install-3u8xm43a/flit/
----------------------------------------
ERROR: Command "/home/sylvain/miniconda3/bin/python /home/sylvain/miniconda3/lib/python3.7/site-packages/pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-2yzid3qp/overlay --no-warn-script-location --no-binary :all: --only-binary :none: -i https://pypi.org/simple -- flit" failed with error code 1 in None
----------------------------------------
ERROR: Command "/home/sylvain/miniconda3/bin/python /home/sylvain/miniconda3/lib/python3.7/site-packages/pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-k0hs5oyp/overlay --no-warn-script-location --no-binary :all: --only-binary :none: -i https://pypi.org/simple -- setuptools wheel 'ipython>=5' 'jupyter_core>=4.2' jupyter_client" failed with error code 1 in None
```