Support -masm= flag for x86 targets.

`clang -S -o - file.c -masm=att` will write assembly to stdout in at&t syntax
(the default), `-masm=intel` will instead output intel style asm.

llvm-svn: 208683
diff --git a/clang/test/Driver/masm.c b/clang/test/Driver/masm.c
new file mode 100644
index 0000000..e9e4422
--- /dev/null
+++ b/clang/test/Driver/masm.c
@@ -0,0 +1,12 @@
+// RUN: %clang -target i386-unknown-linux -masm=intel %s -S -o - | FileCheck --check-prefix=CHECK-INTEL %s
+// RUN: %clang -target i386-unknown-linux -masm=att %s -S -o - | FileCheck --check-prefix=CHECK-ATT %s
+// RUN: not %clang -target i386-unknown-linux -masm=somerequired %s -S -o - 2>&1 | FileCheck --check-prefix=CHECK-SOMEREQUIRED %s
+// RUN: %clang -target arm-unknown-eabi -masm=intel %s -S -o - 2>&1 | FileCheck --check-prefix=CHECK-ARM %s
+
+int f() {
+// CHECK-ATT: movl	$0, %eax
+// CHECK-INTEL: mov	eax, 0
+// CHECK-SOMEREQUIRED: error: unsupported argument 'somerequired' to option 'masm='
+// CHECK-ARM: warning: argument unused during compilation: '-masm=intel'
+  return 0;
+}