[ELF] - Fixed padding for CIE/FDE entries of .eh_frame section

Spec says both CIE/FDE has "Padding
Extra bytes to align the CIE structure to an addressing unit size boundary."
https://refspecs.linuxfoundation.org/LSB_3.0.0/LSB-PDA/LSB-PDA/ehframechpt.html

Patch aligns CIE/FDE entries to the size of platform pointer.

Differential revision: http://reviews.llvm.org/D15637

llvm-svn: 256141