Run CI with LLVM 15 on Windows

This includes changes:

- Adding the Windows LLVM 15 config to the Azure setup.
- Converting the commands in the Azure pipeline file to a call to the
  setup_conda_environment.cmd script (it's easier to edit a script
  rather than individual lines in the Azure file).
- Installation of LLVM 15 from conda-forge.
- A workaround / supporting change for the conda-forge solution to
  conda-forge/llvmdev-feedstock#175.

buildscripts/azure/azure-windows.yml

@@ -22,6 +22,10 @@ jobs:
         PYTHON: '3.12'
         CONDA_ENV: cienv
 
+      llvm15:
+        PYTHON: '3.12'
+        CONDA_ENV: cienv
+        LLVM: '15'
 
   steps:
 
@@ -33,11 +37,7 @@ jobs:
 
     - script: |
         call C:\Miniconda3\Scripts\activate.bat
-        call conda list
-        call conda remove --all -q -y -n %CONDA_ENV%
-        call conda create -n %CONDA_ENV% -q -y python=%PYTHON% cmake
-        call activate %CONDA_ENV%
-        call conda install -y -q -c numba/label/dev llvmdev="14.*" libxml2
+        call buildscripts\\incremental\\setup_conda_environment.cmd
       displayName: 'Before Install'
 
     - script: |

buildscripts/incremental/build.cmd

@@ -1,4 +1,23 @@
 
 call activate %CONDA_ENV%
 
+@rem LLVM derives the location of diaguids.lib from the build-time environment.
+@rem Conda-forge packaging works around this by substituting the build-time
+@rem location of Visual Studio with $ENV{VSINSTALLDIR}. In order to ensure that
+@rem this environment variable is set appropriately, we activate the Visual
+@rem Studio Developer Command Prompt prior to running setup.py
+@rem
+@rem This workaround is required whilst using LLVM from conda-forge; it may also
+@rem be necessary to consider a workaround for our own llvmdev packages.
+@rem
+@rem For more info, see:
+@rem
+@rem - https://github.com/conda-forge/llvmdev-feedstock/issues/175
+@rem - https://github.com/conda-forge/llvmdev-feedstock/pull/223
+@rem - https://github.com/MicrosoftDocs/visualstudio-docs/issues/7774
+if "%LLVM%"=="15" (
+  call "C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\Common7\Tools\VsDevCmd.bat"
+  if %errorlevel% neq 0 exit /b %errorlevel%
+)
+
 python setup.py build

buildscripts/incremental/setup_conda_environment.cmd

@@ -1,24 +1,24 @@
-@rem The cmd /C hack circumvents a regression where conda installs a conda.bat
-@rem script in non-root environments.
-set CONDA_INSTALL=cmd /C conda install -q -y
-set PIP_INSTALL=pip install -q
-
 @echo on
 
-@rem Deactivate any environment
-call deactivate
 @rem Display root environment (for debugging)
-conda list
+call conda list
+
 @rem Clean up any left-over from a previous build
-conda remove --all -q -y -n %CONDA_ENV%
+call conda remove --all -q -y -n %CONDA_ENV%
 
 @rem Create and populate environment
-conda create -n %CONDA_ENV% -q -y python=%PYTHON% cmake
+call conda create -n %CONDA_ENV% -q -y python=%PYTHON% cmake
 if %errorlevel% neq 0 exit /b %errorlevel%
 
 call activate %CONDA_ENV%
 if %errorlevel% neq 0 exit /b %errorlevel%
 
 @rem Install llvmdev
-%CONDA_INSTALL% -c numba/label/dev llvmdev="14.*"
+if "%LLVM%"=="15" (
+  set LLVMDEV_CHANNEL="conda-forge"
+) else (
+  set LLVMDEV_CHANNEL="numba/label/dev"
+)
+
+call conda install -y -q -c %LLVMDEV_CHANNEL% llvmdev="%LLVM%" libxml2
 if %errorlevel% neq 0 exit /b %errorlevel%