[ELF] - Fixed handling relocations against zero sized .eh_frame section.

The file crtbeginT.o has relocations pointing to the start of an empty
.eh_frame that is known to be the first in the link. It does that to
identify the start of the output .eh_frame. Handle this special case.

Differential revision: http://reviews.llvm.org/D15610

llvm-svn: 256414