[PECOFF] Add /manifestfile command line option.

/manifestfile:<path> specifies an alternative manifest file output path.
Default is "<output-path>.manifest" where <output-path> is the executable's
path.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@193195 91177308-0d34-0410-b5e6-96231b3b80d8