Allow -MF to be used in combination with -E -M or -E -MM.

Fixes PR13851. Patch by Dimitry Andric!

llvm-svn: 164717
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index f77d8ee..12564b4 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -219,11 +219,11 @@
       (A = Args.getLastArg(options::OPT_MMD))) {
     // Determine the output location.
     const char *DepFile;
-    if (Output.getType() == types::TY_Dependencies) {
-      DepFile = Output.getFilename();
-    } else if (Arg *MF = Args.getLastArg(options::OPT_MF)) {
+    if (Arg *MF = Args.getLastArg(options::OPT_MF)) {
       DepFile = MF->getValue(Args);
       C.addFailureResultFile(DepFile);
+    } else if (Output.getType() == types::TY_Dependencies) {
+      DepFile = Output.getFilename();
     } else if (A->getOption().matches(options::OPT_M) ||
                A->getOption().matches(options::OPT_MM)) {
       DepFile = "-";