Windows/Clang: Support PDB when cross-compiling

When cross-compiling for Windows on Linux using Clang (with MSVC runtime) CMake claims that the linker does not support PDB files.

CMake Error:
  Error evaluating generator expression:

    $<TARGET_PDB_FILE:target>

  TARGET_PDB_FILE is not supported by the target linker.

And that is definitively wrong because it generates PDB files. However, the $<TARGET_PDB_FILE:...> generator-expression did not know so.

The simple change in this merge-request fixes this.

Backport: release
Topic-rename: clang-cross-compile-windows-pdb