Installation (`stack install` after `git clone`) failure under Windows 10

I'm following the suggested installation instructions, under Windows 10, by entering the following commands at a Git MINGW64 terminal prompt:

- `git clone https://github.com/jgm/gitit`
- `pushd gitit`
- `stack install`

and getting this:

```
{snip}
Cabal > [219 of 220] Compiling Distribution.Simple.Doctest
Cabal > [220 of 220] Compiling Distribution.Simple
Cabal > copy/register
Cabal > Installing library in C:\sr\snapshots\67f8afe8\lib\x86_64-windows-ghc-8.6.5\Cabal-2.4.1.0-5rQrtDcYhR2LOcYye7obEr
Cabal > Registering library for Cabal-2.4.1.0..

-- While building package sendfile-0.7.11.1 using:
C:\sr\setup-exe-cache\x86_64-windows\Cabal-simple_Z6RU0evB_2.4.0.1_ghc-8.6.5.exe --builddir=.stack-work\dist\e626a42b build --ghc-options " -fdiagnostics-color=always"
Process exited with code: ExitFailure 1
Progress 75/157
```

I tried running the `stack install` command in a _Cygwin_ command shell, instead, and got:

```
{snip}
attoparsec > [20 of 21] Compiling Data.Attoparsec.Char8
attoparsec > [21 of 21] Compiling Data.Attoparsec
attoparsec > copy/register
attoparsec > Installing library in C:\sr\snapshots\67f8afe8\lib\x86_64-windows-ghc-8.6.5\attoparsec-0.13.2.3-GA
4ycFABWuC8tgunM2kJRL
attoparsec > Registering library for attoparsec-0.13.2.3..

-- While building package sendfile-0.7.11.1 using:
C:\sr\setup-exe-cache\x86_64-windows\Cabal-simple_Z6RU0evB_2.4.0.1_ghc-8.6.5.exe --builddir=.stack-work\dist\e626a
42b build --ghc-options " -fdiagnostics-color=always"
Process exited with code: ExitFailure 1
Progress 13/83
```

Attempting the `stack install` command from a Windows command prompt yields a similar result.

Scanning all 3 transcripts for _errors_ (They all produce many _warnings_.) yields:

**MINGW64:**

```
cmark-gfm > cbits\tasklist.c:17:17: error:
cmark-gfm > |
cmark-gfm > 17 | if (!node || ((int)node->as.opaque != CMARK_TASKLIST_CHECKED && (int)node->as.opaque != CMARK_TASKLIST_NOCHECKED))
cmark-gfm > | ^
```

```
cmark-gfm > cbits\tasklist.c:17:67: error:
cmark-gfm > |
cmark-gfm > 17 | if (!node || ((int)node->as.opaque != CMARK_TASKLIST_CHECKED && (int)node->as.opaque != CMARK_TASKLIST_NOCHECKED))
cmark-gfm > | ^
```

{Omitted 2 more like the above, from the same file.}

```
sendfile > src\Network\Socket\SendFile\Win32.hsc:103:1: error:
sendfile > |
sendfile > 103 | foreign import ccall unsafe "io.h _get_osfhandle"
sendfile > | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^...
```

**Cygwin:**

(Contains only the last error reported above.)

**CMD:**

Same as above, but with additional diagnostic information:

```
sendfile > src\Network\Socket\SendFile\Win32.hsc:103:1: error:
sendfile > * Unacceptable result type in foreign declaration:
sendfile > `IntPtr' cannot be marshalled in a foreign call
sendfile > because its data constructor is not in scope
sendfile > Possible fix: import the data constructor to bring it into scope
sendfile > * When checking declaration:
sendfile > foreign import ccall unsafe "io.h _get_osfhandle" c_get_osfhandle
sendfile > :: Fd -> IO IntPtr
sendfile > |
sendfile > 103 | foreign import ccall unsafe "io.h _get_osfhandle"
sendfile > | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^...
```

Oh, I just noticed this, at the very start of my console output:

```
WARNING: Ignoring sendfile's bounds on Win32 (>=2.2.0.0 && <2.3); using Win32-2.6.1.0.
Reason: allow-newer enabled.
```