[sparc] Use of -fcall-used-* flags in Makefile?

[Koakuma]

Hello, first time poster so apologies if I posted to the wrong list.

Anyone knows why the SPARC makefiles (arch/sparc/Makefile and
arch/sparc/vdso/Makefile) set `-fcall-used-g5` and  `-fcall-used-g7`
in their CFLAGS?
Would it be safe if the kernel is compiled without those flags?

The context is that there's an effort to make the sparc64 kernel build
under LLVM/clang, and if possible we'd like to build the kernel without
those flags, at least when building with clang, since it simplifies
a lot of things on the LLVM side.
(LLVM tracker: https://github.com/llvm/llvm-project/issues/40792)