MSVC: Support using clang build used by clc to build whole Mesa

buildscript/modules/clang.cmd

@@ -1,24 +1,28 @@
 @rem Detect clang
 @setlocal
 @set clangstate=0
+@IF %toolchain%==msvc IF EXIST "%devroot%\llvm\build\%abi%\bin\clang-cl.exe" set clangstate=1
 @IF %toolchain%==msvc IF %abi%==x64 IF EXIST "%ProgramFiles%\LLVM\bin\clang-cl.exe" set clangstate=1
 @IF %toolchain%==msvc IF %abi%==x86 IF /I %PROCESSOR_ARCHITECTURE%==AMD64 IF EXIST "%ProgramFiles% (x86)\LLVM\bin\clang-cl.exe" set clangstate=1
 @IF %toolchain%==msvc IF %abi%==x86 IF /I %PROCESSOR_ARCHITECTURE%==x86 IF EXIST "%ProgramFiles%\LLVM\bin\clang-cl.exe" set clangstate=1
-@IF %toolchain%==msvc set clangstate=0
 @IF NOT %toolchain%==msvc set clangstate=1
 
 @set useclang=n
 @IF %clangstate% GTR 0 set /p useclang=Use clang compiler with selected toolchain ^(y/n^):
 @IF %clangstate% GTR 0 echo.
 @endlocal&set useclang=%useclang%
 
-@if /I "%useclang%"=="y" IF %toolchain%==msvc IF %abi%==x64 set PATH=%ProgramFiles%\LLVM\bin\;%PATH%
-@if /I "%useclang%"=="y" IF %toolchain%==msvc IF %abi%==x86 IF /I %PROCESSOR_ARCHITECTURE%==AMD64 set PATH=%ProgramFiles% (x86)\LLVM\bin\;%PATH%
-@if /I "%useclang%"=="y" IF %toolchain%==msvc IF %abi%==x86 IF /I %PROCESSOR_ARCHITECTURE%==x86 set PATH=%ProgramFiles%\LLVM\bin\;%PATH%
+@set llvmalreadyloaded=0
+@if /I "%useclang%"=="y" IF %toolchain%==msvc IF EXIST "%devroot%\llvm\build\%abi%\bin\clang-cl.exe" set PATH=%devroot%\llvm\build\%abi%\bin\;%PATH%
+@if /I "%useclang%"=="y" IF %toolchain%==msvc IF EXIST "%devroot%\llvm\build\%abi%\bin\clang-cl.exe" set llvmalreadyloaded=1
+@if /I "%useclang%"=="y" IF %toolchain%==msvc IF %abi%==x64 IF NOT EXIST "%devroot%\llvm\build\%abi%\bin\clang-cl.exe" set PATH=%ProgramFiles%\LLVM\bin\;%PATH%
+@if /I "%useclang%"=="y" IF %toolchain%==msvc IF %abi%==x86 IF /I %PROCESSOR_ARCHITECTURE%==AMD64 IF NOT EXIST "%devroot%\llvm\build\%abi%\bin\clang-cl.exe" set PATH=%ProgramFiles% (x86)\LLVM\bin\;%PATH%
+@if /I "%useclang%"=="y" IF %toolchain%==msvc IF %abi%==x86 IF /I %PROCESSOR_ARCHITECTURE%==x86 IF NOT EXIST "%devroot%\llvm\build\%abi%\bin\clang-cl.exe" set PATH=%ProgramFiles%\LLVM\bin\;%PATH%
 @if /I "%useclang%"=="y" IF %toolchain%==msvc set CC=clang-cl.exe
 @if /I "%useclang%"=="y" IF %toolchain%==msvc set CXX=clang-cl.exe
 @if /I "%useclang%"=="y" IF NOT %toolchain%==msvc set MSYSTEM=CLANG%MSYSTEM:~-2%
 @if /I "%useclang%"=="y" IF NOT %toolchain%==msvc set LMSYSTEM=clang%MSYSTEM:~-2%
 @if /I "%useclang%"=="y" IF NOT %toolchain%==msvc set toolchain=clang
 @if /I "%useclang%"=="y" set TITLE=%TITLE% with clang compiler
-@if /I "%useclang%"=="y" TITLE %TITLE%
+@if /I "%useclang%"=="y" TITLE %TITLE%
+@set useclang=

buildscript/modules/mesa3d.cmd

@@ -181,7 +181,7 @@
 @if /I NOT "%llvmless%"=="y" IF %llvmmethod%==cmake set buildconf=%buildconf% --cmake-prefix-path="%devroot:\=/%/llvm/build/%abi%"
 @if /I NOT "%llvmless%"=="y" IF %llvmmethod%==cmake IF %cmakestate% EQU 1 SET PATH=%devroot%\cmake\bin\;%PATH%
 @if /I NOT "%llvmless%"=="y" IF NOT %llvmmethod%==cmake set buildconf=%buildconf% --cmake-prefix-path=
-@if /I NOT "%llvmless%"=="y" IF NOT %llvmmethod%==cmake IF %toolchain%==msvc SET PATH=%devroot%\llvm\build\%abi%\bin\;%PATH%
+@if /I NOT "%llvmless%"=="y" IF NOT %llvmmethod%==cmake IF %toolchain%==msvc if %llvmalreadyloaded% EQU 0 SET PATH=%devroot%\llvm\build\%abi%\bin\;%PATH%
 @if /I "%llvmless%"=="y" set buildconf=%buildconf% -Dllvm=%mesonboolfalse%
 
 @set useninja=n

releasenotes.md

@@ -6,8 +6,8 @@
 - MSYS2: Change currrent directory to Windows current folder;
 - MSYS2/Meson: Don't hardcode source code directory;
 - MSYS2: Restore option to clear package cache after installing packages;
-- MSVC: Prepare to use clang build used by clc to build whole Mesa;
-- OpenCL stack: Make sure we never link against clang-cpp library.
+- OpenCL stack: Make sure we never link against clang-cpp library;
+- MSVC: Support using clang build used by clc to build whole Mesa.
 ### Distribution
 - MSYS2: Strip lib prefix from Microsoft CLC filename [22.2+].
 # 22.1.5