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
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 3053d9b..526968c 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -338,6 +338,7 @@
   }
 
   Args.AddLastArg(CmdArgs, options::OPT_MP);
+  Args.AddLastArg(CmdArgs, options::OPT_MV);
 
   // Convert all -MQ <target> args to -MT <quoted target>
   for (arg_iterator it = Args.filtered_begin(options::OPT_MT,