GCOV: Expose the -coverage-exit-block-before-body flag in clang -cc1

This exposes the optional exit block placement logic from r232438 as a
clang -cc1 option. There is a test on the llvm side, but there isn't
really a way to inspect the gcov options from clang to test it here as
well.

llvm-svn: 232439

clang/lib/Frontend/CompilerInvocation.cpp

@@ -494,6 +494,8 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
     Opts.CoverageExtraChecksum = Args.hasArg(OPT_coverage_cfg_checksum);
     Opts.CoverageNoFunctionNamesInData =
         Args.hasArg(OPT_coverage_no_function_names_in_data);
+    Opts.CoverageExitBlockBeforeBody =
+        Args.hasArg(OPT_coverage_exit_block_before_body);
     if (Args.hasArg(OPT_coverage_version_EQ)) {
       StringRef CoverageVersion = Args.getLastArgValue(OPT_coverage_version_EQ);
       if (CoverageVersion.size() != 4) {