[AArch64][X86] Allow 64-bit label differences lower to IMAGE_REL_*_REL32

`IMAGE_REL_ARM64_REL64/IMAGE_REL_AMD64_REL64` do not exist and `.quad a - .` is
currently not representable.

For instrumentation, `.quad a - .` is useful representing a cross-section
reference in a metadata section, to allow ELF medium/large code models. The COFF
limitation makes such generic instrumentations inconvenient. I plan to make a
PGO/coverage metadata section field relative in D104556.

Differential Revision: https://reviews.llvm.org/D104564