Using Anaconda Python and Qt module - Windows. Error with finding QT due to PATH

With the environment setup to have the Qt location on the path (i.e. `C:\Qt\5.8\msvc2015_64\bin`), meson will not find this correctly when running meson with the Anaconda distribution of python.

This is because Anaconda will prepend `C:\Anaconda3\Library\bin` to the `PATH` when it runs.

This means that on line 453 of `dependencies/base.py`:
` command = shutil.which(name)`

Will find the Qt files that exist in that folder when looking for qmake, not the Qt in C:\Qt....

This issue does not occur with the other python I have available, which does not prepend to `PATH`.

Start with dependencies/base.py at line 453 and inspect how shutil.which(name) selects qmake. Reproduce the lookup on Windows with Anaconda Python, C:\Anaconda3\Library\bin first in PATH, and Qt at C:\Qt\5.8\msvc2015_64\bin. Done means Meson finds the intended Qt tools in this setup without regressing normal Python behavior.

Written by the indexing model from the issue text.