[clang] [driver] Do not warn about unused plugin flags. (PR #88948)

[Fangrui Song via cfe-commits]

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@@ -0,0 +1,5 @@
+// RUN: %clang -### -c -fpass-plugin=bar.so -fplugin=bar.so -fplugin-arg-bar-option -Werror %s 2>&1 | FileCheck %s
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MaskRay wrote:

This can be moved to `Driver/plugin-driver-args.cpp` with `%clang -### -c -x assembler`

https://github.com/llvm/llvm-project/pull/88948