[clang] [flang] [flang][Driver] Add -masm option to flang (PR #81490)

[Fangrui Song via cfe-commits]

================
@@ -0,0 +1,13 @@
+// RUN: %flang -target x86_64-unknown-linux -masm=intel -S %s -### 2>&1 | FileCheck --check-prefix=CHECK-INTEL %s
----------------
MaskRay wrote:

`--target=` for new tests

https://github.com/llvm/llvm-project/pull/81490