[GCOV] Set !kcfi_type metadata for indirectly called functions

With CONFIG_GCOV_KERNEL, the Linux kernel indirectly calls the
__llvm_gcov_* functions generated by LLVM. With -fsanitize=kcfi,
these calls are made from instrumented code and fail indirect
call checks as they don't have !kcfi_type metadata. Similarly
to D138945, set type metadata for these functions to allow GCOV
and KCFI to be both enabled.

Link: https://github.com/ClangBuiltLinux/linux/issues/1778

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D141444