[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 passes args to -cc1as.
+// RUN: %clang -### -Xclangas -target-feature -Xclangas +v5t %s 2>&1 | \
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MaskRay wrote:

change one arg to use `-Xclangas=`

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