Makefile: check for --exclude-libs

While writing to the dynsym is futile, the --exclude-libs options is not
recognized by all linkers (e.g. riscv64-elf-ld.bfd).

Signed-off-by: Leon M. Busch-George <leon@georgemail.eu>
Reviewed-by: Anup Patel <anup@brainfault.org>