[llvm] [clang][ARM] Enable --print-supported-extensions for ARM (PR #66083)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> `./bin/clang -target arm-linux-gnueabihf --print-supported-extensions`

Consider switching to `--target=` since `-target ` has been deprecated since Clang 3.4.

https://github.com/llvm/llvm-project/pull/66083