[ELF] - improved relocation-copy.s test (added R_X86_64_32 relocations)

* Added instructions to generate R_X86_64_32 relocations. Without that next part of code was uncovered by test, code worked without it:
bool X86_64TargetInfo::relocNeedsPlt(uint32_t Type, const SymbolBody &S) const {
  if (needsCopyRel(Type, S))
    return false;
* Removed -e main, added _start

Differential revision: http://reviews.llvm.org/D15714

llvm-svn: 257331