Extended Description

As reported by Jeroen here: http://lists.llvm.org/pipermail/cfe-dev/2019-September/063225.html

clang 9 does not seem to be able to open files using relative paths on mapped drives.

For example:

mkdir \src\tmp\foo
net use x: \localhost\c$\src\tmp\foo
gvim x:\a.c
x:
c:\src\llvm.monorepo\build.release\bin\clang-cl /c a.c
clang-cl: error: no such file or directory: 'a.c'

clang 8 did not have this problem.