Add support for the /EP argument to clang-cl

This maps the /EP argument to both -E and -P.

Patch by Ehsan Akhgari!

Differential Reviion: http://reviews.llvm.org/D4133

llvm-svn: 210935
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 67e0122..1a9de3a 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -152,9 +152,10 @@
   Arg *PhaseArg = nullptr;
   phases::ID FinalPhase;
 
-  // -{E,M,MM} and /P only run the preprocessor.
+  // -{E,EP,P,M,MM} only run the preprocessor.
   if (CCCIsCPP() ||
       (PhaseArg = DAL.getLastArg(options::OPT_E)) ||
+      (PhaseArg = DAL.getLastArg(options::OPT__SLASH_EP)) ||
       (PhaseArg = DAL.getLastArg(options::OPT_M, options::OPT_MM)) ||
       (PhaseArg = DAL.getLastArg(options::OPT__SLASH_P))) {
     FinalPhase = phases::Preprocess;