PDB error when compiling graal/substratevm/com.oracle.svm.native.libchelper

When compiling graal/substractevm/com.oracle.svm.native.libchelper on Windows using latest Windows SDK I get this errors:

FAILED: cl -nologo -showIncludes -Ic:\graal\substratevm\src\com.oracle.svm.native.libchelper\include -Zi -O2 -D_LITTLE_ENDIAN -c c:\graal\substratevm\src\com.oracle.svm.native.libchelper\src\cSunMiscSignal.c -Fosrc\cSunMiscSignal.obj c:\graal\substratevm\src\com.oracle.svm.native.libchelper\src\cSunMiscSignal.c: fatal error C1041: cannot open program database 'c:\graal\substratevm\mxbuild\windows-amd64\src\com.oracle.svm.native.libchelper\vc140.pdb'; if multiple CL.EXE write to the same .PDB file, please use /FS

If I keep running mx build it will eventually work.
The issue is that ninja is trying to compile the files concurrently which causes cl.exe to try and output PDB to the same file (vc140.pdb).
Need to add /Fd option to cl.exe to avoid using same file.

Start with the mx build definition and generated command for graal/substratevm/com.oracle.svm.native.libchelper, especially the cl invocation compiling cSunMiscSignal.c. Reproduce with a concurrent Windows build and verify that parallel cl.exe invocations no longer share vc140.pdb; rerun mx build to confirm compilation completes without retries.