Add support to -Wa,-W in clang

[jcai19]

Summary

Currently clang does not support -Wa,-W, which suppresses warning
messages in GNU assembler. Add this option for gcc compatibility.
https://bugs.llvm.org/show_bug.cgi?id=43651

[jcai19]

Fix typos.

[jcai19]

Update test cases.

[bcain]

LGTM

[jcai19]

For autogenerated comment log.

[MaskRay]

clang/test/Driver/as-w-option.c

1

Reusing the existing as-no-warnings.c may be better. I've moved the UN lines there.

clang/lib/Driver/ToolChains/Clang.cpp

for (StringRef Value : A->getValues()) {
       }
 
       if (Value == "-force_cpusubtype_ALL") {
         // Do nothing, this is the default and we don't support anything else.
       } else if (Value == "-L") {
         CmdArgs.push_back("-msave-temp-labels");
       } else if (Value == "--fatal-warnings") {
         CmdArgs.push_back("-massembler-fatal-warnings");
-      } else if (Value == "--no-warn") {
+      } else if (Value == "--no-warn" || Value == "-W") {
         CmdArgs.push_back("-massembler-no-warn");
       } else if (Value == "--noexecstack") {
         UseNoExecStack = true;
       } else if (Value.startswith("-compress-debug-sections") ||
                  Value.startswith("--compress-debug-sections") ||
                  Value == "-nocompress-debug-sections" ||
                  Value == "--nocompress-debug-sections") {
         CmdArgs.push_back(Value.data());

clang/test/Driver/as-w-option.c

+// RUN: %clang -### %s -c -o tmp.o -fno-integrated-as -Wa,-W 2>&1 | FileCheck -check-prefix=CHECK-NOIAS %s
+// RUN: %clang -### %s -c -o tmp.o -integrated-as -Wa,-W 2>&1 | FileCheck -check-prefix=CHECK-IAS %s
+// RUN: %clang %s -c -o %t.o -integrated-as -Wa,-W 2>&1 | FileCheck -allow-empty --check-prefix=CHECK-AS-NOWARN %s
+// RUN: %clang %s -c -o %t.o -fno-integrated-as -Wa,-W 2>&1 | FileCheck -allow-empty --check-prefix=CHECK-AS-NOWARN %s
+// RUN: not %clang %s -c -o %t.o -integrated-as -Wa,--fatal-warnings 2>&1 | FileCheck --check-prefix=CHECK-AS-FATAL %s
+// RUN: not %clang %s -c -o %t.o -fno-integrated-as -Wa,--fatal-warnings 2>&1 | FileCheck --check-prefix=CHECK-AS-FATAL %s
+
+// CHECK-IAS: "-cc1" {{.*}} "-massembler-no-warn"
+// CHECK-NOIAS: "-W"
+// CHECK-AS-NOWARN-NOT: warning:
+// CHECK-AS-FATAL-NOT: warning:
+// CHECK-AS-FATAL: error
+
+__asm(".warning");