[clang] Apply cfi_unchecked_callee rules to -fsanitize=function (#170725)
Allow the normal rules for preventing instrumentation on indirect calls
to `cfi_unchecked_callee` function types and `cfi_unchecked_callee`
functions when using `-fsanitize=function`. While it's technically
separate from `-fsanitize=cfi`, this particular UBSan mode checks for
similar control flow bugs so it makes sense to also prevent those
control flow checks from being added onto `cfi_unchecked_callee`
functions.