Fix production of R_X86_64_GOTPCRELX/R_X86_64_REX_GOTPCRELX.

We were producing R_X86_64_GOTPCRELX for invalid instructions and
sometimes producing R_X86_64_GOTPCRELX instead of
R_X86_64_REX_GOTPCRELX.

llvm-svn: 271118
8 files changed