A set of x86 fixes: - Use SYM_FUNC_START_WEAK in the mem* ASM functions instead of a combination of .weak and SYM_FUNC_START_LOCAL which makes LLVMs integrated assembler upset. - Correct the mitigation selection logic which prevented the related prctl to work correctly. - Make the UV5 hubless system work correctly by fixing up the malformed table entries and adding the missing ones.