PR23653, ld SIGSEGVs when attempts to link sparc object with x86_64 library

PR23653, ld SIGSEGVs when attempts to link sparc object with x86_64 library

This patch improves dynobj selection.  This allows the testcase in the
PR to proceed further before segfaulting due to other bugs in the
sparc backend.

../ld/ld-new --eh-frame-hdr -m elf_x86_64 -shared -o bug.so.5 bug.o ./libc.so.6 ./crtendS.o
../ld/ld-new: sparc architecture of input file `bug.o' is incompatible with i386:x86-64 output
../ld/ld-new: bug.o: in function `a':
bug.c:(.text+0x4): undefined reference to `_GLOBAL_OFFSET_TABLE_'
../ld/ld-new: bug.c:(.text+0x8): undefined reference to `_GLOBAL_OFFSET_TABLE_'
Segmentation fault

	PR 23653
	* elflink.c (_bfd_elf_link_create_dynstrtab): Match elf_object_id
	too when choosing dynobj.