clang-cl: Support the run-time selection options (/MD, /MT et al.)

These flags set some preprocessor macros and injects a dependency
on the runtime library into the object file, which later is picked up
by the linker.

This also adds a new CC1 flag for adding a dependent library.

Differential Revision: http://llvm-reviews.chandlerc.com/D1315

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187945 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/clang/Driver/CC1Options.td b/include/clang/Driver/CC1Options.td
index fdc073b..6ac40f5 100644
--- a/include/clang/Driver/CC1Options.td
+++ b/include/clang/Driver/CC1Options.td
@@ -210,6 +210,8 @@
   HelpText<"Run the SLP vectorization passes">;
 def vectorize_slp_aggressive : Flag<["-"], "vectorize-slp-aggressive">,
   HelpText<"Run the BB vectorization passes">;
+def dependent_lib : Joined<["--"], "dependent-lib=">,
+  HelpText<"Add dependent library">;
 
 //===----------------------------------------------------------------------===//
 // Dependency Output Options