[ELF] relocateNonAlloc: clean up workaround code

relocateNonAlloc is costly for .debug_* section relocating. We don't
want to burn CPU cycles on other targets' workarounds.

Remove a temporary workaround for Linux objtool after a proper fix
https://git.kernel.org/linus/b8ec60e1186cdcfce41e7db4c827cb107e459002

Move the R_386_GOTPC workaround for GCC<8 beside the R_PC workaround.