[msan] -fsanitize-memory-track-origins=[level] flag and docs.

This change turns -fsanitize-memory-track-origins into
-fsanitize-memory-track-origins=[level] flag (keeping the old one for
compatibility). Possible levels are 0 (off), 1 (default) and 2 (incredibly
detailed). See docs (part of this patch) for more info.

llvm-svn: 204346

clang/lib/Frontend/CompilerInvocation.cpp

@@ -451,9 +451,9 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.LinkBitcodeFile = Args.getLastArgValue(OPT_mlink_bitcode_file);
   Opts.SanitizerBlacklistFile = Args.getLastArgValue(OPT_fsanitize_blacklist);
   Opts.SanitizeMemoryTrackOrigins =
-    Args.hasArg(OPT_fsanitize_memory_track_origins);
+      getLastArgIntValue(Args, OPT_fsanitize_memory_track_origins_EQ, 0, Diags);
   Opts.SanitizeUndefinedTrapOnError =
-    Args.hasArg(OPT_fsanitize_undefined_trap_on_error);
+      Args.hasArg(OPT_fsanitize_undefined_trap_on_error);
   Opts.SSPBufferSize =
       getLastArgIntValue(Args, OPT_stack_protector_buffer_size, 8, Diags);
   Opts.StackRealignment = Args.hasArg(OPT_mstackrealign);