Reland "[llvm][llvm-objcopy] Added support for outputting to binary in llvm-objcopy"

Reland "[llvm][llvm-objcopy] Added support for outputting to binary in llvm-objcopy"

This change adds the "-O binary" flag which directs llvm-objcopy to
output the object file to the same format as GNU objcopy does when given
the flag "-O binary". This was done by splitting the Object class into
two subclasses ObjectELF and ObjectBianry which each output a different
format but relay on the same code to read in the Object in Object.

Patch by Jake Ehrlich

Differential Revision: https://reviews.llvm.org/D34480

llvm-svn: 310018