mips regression fixes

mips regression fixes

Commit 54fbc12d64 introduced mips-linux testsuite regressions.
+FAIL: MIPS magic __ehdr_start symbol test 1 (o32)
+FAIL: PR ld/21334 MIPS GOT16 relocation in static binary
+FAIL: PR ld/21375 in SVR4 executable (hidden)
These are all assertion failures in mips_elf_sort_hash_table
  BFD_ASSERT (hsd.max_local_dynindx <= htab->root.local_dynsymcount + 1);

This was a pre-existing problem exposed by commit 54fbc12d64.

	* elfxx-mips.c (mips_elf_sort_hash_table): Properly test for
	no dynsyms.