[modules] When writing a module file built with -fmodule-map-file-home-is-cwd,

via a module map found by -fmodule-map-file=, the home directory of the module
is the current working directory, even if that's a different directory on
reload.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@244988 91177308-0d34-0410-b5e6-96231b3b80d8