Clarify R_X86_64_REX_GOTPCRELX transformation
Instructions on memory operand with _GOTPCRELX relocations against symbol, foo, can be transformed into a different form on immediate operand if foo is defined locally and the relocation addend is -4:
movl foo@GOTPCREL(%rip), %eax
For
movl foo@GOTPCREL+4(%rip), %eax
The transformation is invalid since the relocation addend is 0.