[clang] [flang] [flang][Driver] Support -print-supported-extensions (PR #117402)

[Andrzej Warzyński via cfe-commits]

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@@ -0,0 +1,34 @@
+! REQUIRES: arm-registered-target
+
+! RUN: %flang --target=arm-linux-gnu --print-supported-extensions 2>&1 \
+! RUN:   | FileCheck --strict-whitespace --implicit-check-not=FEAT_ %s
+
+! CHECK: All available -march extensions for ARM
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banach-space wrote:

I don't have a better suggestion. I do recall similar situation in the past and being recommended to use that file. I do feel though that it would be worthwhile creating a dedicated cpp file for this kind of things. 

Once you update this PR, we can ping Clang driver code-owner.

https://github.com/llvm/llvm-project/pull/117402