[X86] Check immediate before get it.

Authored by LuoYuanke on Jun 10 2021, 7:50 AM.


[X86] Check immediate before get it.

For CMP imm instruction, when the operand 1 is symbol address we should
check if it is immediate first. Here is the example code.
`CMP64mi32 $noreg, 8, killed renamable $rcx, @d, $noreg, @a, implicit-def
Many thanks to Craig, Topper for the test case to reproduce this issue.

Differential Revision: https://reviews.llvm.org/D104037