LoongArch: gas: Simplify relocations in sections without code flag

LoongArch: gas: Simplify relocations in sections without code flag

Gas should not emit ADD/SUB relocation pairs for label differences
if they are in the same section without code flag even relax enabled.
Because the real value is not be affected by relaxation and it can be
compute out in assembly stage. Thus, correct the `TC_FORCE_RELOCATION
_SUB_SAME` and the label differences in same section without code
flag can be resolved in fixup_segment().