[FIXUP] Use Multi-ToolTask in MSVC builds by default

It allows to build as simple as `cmake --build . -j<JOBS>`.

Author: hebasto

CMakeLists.txt

@@ -102,6 +102,9 @@ if(WIN32)
   if(MSVC)
     set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>")
     add_compile_options(/utf-8 /Zc:__cplusplus)
+    # Improve parallelism in MSBuild.
+    # See: https://devblogs.microsoft.com/cppblog/improved-parallelism-in-msbuild/.
+    list(APPEND CMAKE_VS_GLOBALS "UseMultiToolTask=true")
   endif()
 
   if(MINGW)

cmake/optional.cmake

@@ -13,11 +13,10 @@ if(CCACHE)
       set(MSVC_CCACHE_WRAPPER_CONTENT "\"${CCACHE_EXECUTABLE}\" \"${CMAKE_CXX_COMPILER}\"")
       set(MSVC_CCACHE_WRAPPER_FILENAME wrapped-cl.bat)
       file(WRITE ${CMAKE_BINARY_DIR}/${MSVC_CCACHE_WRAPPER_FILENAME} "${MSVC_CCACHE_WRAPPER_CONTENT} %*")
-      set(CMAKE_VS_GLOBALS
+      list(APPEND CMAKE_VS_GLOBALS
         "CLToolExe=${MSVC_CCACHE_WRAPPER_FILENAME}"
         "CLToolPath=${CMAKE_BINARY_DIR}"
         "TrackFileAccess=false"
-        "UseMultiToolTask=true"
         "DebugInformationFormat=OldStyle"
       )
     else()