x86_64_mov_to_lea5.o and x86_64_mov_to_lea6.o must be assembled with
-mrelax-relocations=yes since when assembler is configured with
--disable-x86-relax-relocations, R_X86_64_GOTPCRELX relocation won't
be generated. This linker optimization requires R_X86_64_GOTPCRELX
relocation.
This patch also removed the duplicated x86_64_overflow_pc32.o target.