[llvm] [LLVMgold] Suppress -Wcast-function-type-mismatch diagnostic (PR #89994)

[Usman Nadeem via llvm-commits]

UsmanNadeem wrote:

This change is breaking some of our build bots because `-Wcast-function-type` is only supported in clang 13.0+ 
I am not familiar with this warning but can this be fixed without suppressing the warning, like other patches e.g. https://github.com/llvm/llvm-project/pull/76875 and https://github.com/llvm/llvm-project/pull/86290

> llvm/tools/gold/gold-plugin.cpp:475:32: error: unknown warning group '-Wcast-function-type', ignored [-Werror,-Wunknown-warning-option]
> #pragma GCC diagnostic ignored "-Wcast-function-type"
>                                ^
> 1 error generated.

https://llvm.org/docs/GettingStarted.html#host-c-toolchain-both-compiler-and-standard-library lists Clang 5.0, we are using clang 12.

https://github.com/llvm/llvm-project/pull/89994