Add compilers to conda environment

This fixes issues with `libstdc++.so` when using a system with a newer
compiler. In such cases, the compiler will create links to new symbols,
but the shared library available at runtime from conda-forge will not
have them available.

This results in errors such as:
```
ImportError: /home/elliott/micromamba/envs/mpl-dev/bin/../lib/libstdc++.so.6: version `CXXABI_1.3.15' not found (required by /home/elliott/code/matplotlib/build/cp39/src/_c_internal_utils.cpython-39-x86_64-linux-gnu.so)
```

.appveyor.yml

@@ -68,7 +68,7 @@ install:
 test_script:
   # Now build the thing..
   - set LINK=/LIBPATH:%cd%\lib
-  - pip install -v --no-build-isolation --config-settings=setup-args="--vsenv" --editable .[dev]
+  - pip install -v --no-build-isolation --editable .[dev]
   # this should show no freetype dll...
   - set "DUMPBIN=%VS140COMNTOOLS%\..\..\VC\bin\dumpbin.exe"
   - '"%DUMPBIN%" /DEPENDENTS lib\matplotlib\ft2font*.pyd | findstr freetype.*.dll && exit /b 1 || exit /b 0'

environment.yml

@@ -11,6 +11,8 @@ channels:
 dependencies:
   # runtime dependencies
   - cairocffi
+  - c-compiler
+  - cxx-compiler
   - contourpy>=1.0.1
   - cycler>=0.10.0
   - fonttools>=4.22.0
@@ -24,6 +26,7 @@ dependencies:
   - pygobject
   - pyparsing>=2.3.1
   - pyqt
+  - python
   - python-dateutil>=2.1
   - setuptools_scm
   - wxpython