In generators such as Ninja that can run multiple "cl" processes that
refer to the same compiler .pdb file (/Fd) at the same time, MSVC from
Visual Studio 2013 complains:
fatal error C1041: cannot open program database '.../vc120.pdb';
if multiple CL.EXE write to the same .PDB file, please use /FS
According to "cl /?":
/FS force to use MSPDBSRV.EXE
Add the flag to compilation lines for this compiler version just after the
/Fd option.
Remove the old-style "Windows-cl.cmake" and its helper "cl.cmake". Load
the information through new-style "Platform/Windows-MSVC-<lang>.cmake"
files. Factor information common to C and CXX into a helper file
"Platform/Windows-MSVC.cmake" loaded from the per-language files.
Brad King