Introduce -fsanitize-coverage=N flag

Summary:
This change makes the asan-coverge (formerly -mllvm -asan-coverge)
accessible via a clang flag.
Companion patch to LLVM is http://reviews.llvm.org/D6152

Test Plan: regression tests, chromium

Reviewers: samsonov

Reviewed By: samsonov

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D6153

llvm-svn: 221719
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index add0c9b..6531a40 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -488,6 +488,8 @@
   Opts.CompressDebugSections = Args.hasArg(OPT_compress_debug_sections);
   Opts.DebugCompilationDir = Args.getLastArgValue(OPT_fdebug_compilation_dir);
   Opts.LinkBitcodeFile = Args.getLastArgValue(OPT_mlink_bitcode_file);
+  Opts.SanitizeCoverage =
+      getLastArgIntValue(Args, OPT_fsanitize_coverage, 0, Diags);
   Opts.SanitizeMemoryTrackOrigins =
       getLastArgIntValue(Args, OPT_fsanitize_memory_track_origins_EQ, 0, Diags);
   Opts.SanitizeUndefinedTrapOnError =