[clang] [clang][Driver] Support passing arbitrary args to `-cc1as` with `-Xclangas`. (PR #100714)

[Fangrui Song via cfe-commits]

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@@ -0,0 +1,6 @@
+/// Check that -Xclangas/-Xclangas= are passed to -cc1as.
+// RUN: %clang -### -Xclangas -target-feature -Xclangas=+v5t %s 2>&1 | \
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MaskRay wrote:

Also add a `-Werror` to test `Arg->claim();`. I haven't tested, but without `Arg->claim();` there will be a warning / or error if -Werror

https://github.com/llvm/llvm-project/pull/100714