Support generating NMake/Jom-style depfiles.

NMake is a Make-like builder that comes with Microsoft Visual Studio.
Jom (https://wiki.qt.io/Jom) is an NMake-compatible build tool.
Dependency files for NMake/Jom need to use double-quotes to wrap
filespecs containing special characters, instead of the backslash
escapes that GNU Make wants.

Adds the -MV option, which specifies to use double-quotes as needed
instead of backslash escapes when writing the dependency file.

Differential Revision: http://reviews.llvm.org/D9260

llvm-svn: 235903