Add -expand-relocs to llvm-readobj

This option expands shown relocations from single line to a dictionary
format:

  Relocation {
    Offset: 0x4
    Type: R_386_32 (1)
    Symbol: sym
    Info: 0x0
  }
Add extensive relocation tests for llvm-readobj

This test ensures that relocation type names returned by libObject match
the raw relocation type value.