Add -fno-coverage-mapping flag.

This new flag allows the user to disable a previous instance of
-fcoverage-mapping, if needed.

llvm-svn: 244170
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 31793ea..8934c80 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -456,7 +456,8 @@
       Args.hasArg(OPT_fprofile_instr_generate_EQ);
   Opts.InstrProfileOutput = Args.getLastArgValue(OPT_fprofile_instr_generate_EQ);
   Opts.InstrProfileInput = Args.getLastArgValue(OPT_fprofile_instr_use_EQ);
-  Opts.CoverageMapping = Args.hasArg(OPT_fcoverage_mapping);
+  Opts.CoverageMapping =
+      Args.hasFlag(OPT_fcoverage_mapping, OPT_fno_coverage_mapping, false);
   Opts.DumpCoverageMapping = Args.hasArg(OPT_dump_coverage_mapping);
   Opts.AsmVerbose = Args.hasArg(OPT_masm_verbose);
   Opts.ObjCAutoRefCountExceptions = Args.hasArg(OPT_fobjc_arc_exceptions);