CMakeDetermineCompilerId: Add detection of clang.exe bundled with VS

When using a clang toolset we need to find `clang.exe` instead of
`cl.exe`.

Modules/CMakeDetermineCompilerId.cmake

@@ -157,7 +157,11 @@ Id flags: ${testflags}
     set(vs_version ${CMAKE_MATCH_1})
     set(id_platform ${CMAKE_VS_PLATFORM_NAME})
     set(id_lang "${lang}")
+    if(CMAKE_VS_PLATFORM_TOOLSET MATCHES "v[0-9]+_clang_.*")
+      set(id_cl clang.exe)
+    else()
       set(id_cl cl.exe)
+    endif()
     if(CMAKE_VS_PLATFORM_NAME STREQUAL "Tegra-Android")
       set(v NsightTegra)
       set(ext vcxproj)