[clang] [Clang][Driver] Warn about `-c/-S` with `-fsyntax-only` (PR #98607)

[Fangrui Song via cfe-commits]

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@@ -0,0 +1,9 @@
+// RUN: %clang -fsyntax-only -S %s 2>&1 | FileCheck %s --check-prefix=CHECK-ASM
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MaskRay wrote:

Perhaps just warn-fsyntax-only.c

https://github.com/llvm/llvm-project/pull/98607