Add symbols for global entry stub, and report stats

Add symbols for global entry stub, and report stats

The undefined function symbols (with non-zero value) on global entry
stubs are discarded by objdump when disassembling, so give objdump
another symbol to mark the stubs.

Also fixes a couple of bugs:
- entry_section was set to .opd for ELFv2, which meant a hard error
  rather than a warning when _start wasn't defined.
- global entry stubs were not built if they were the only type of
  stub in an executable.

bfd/
	* elf64-ppc.c (ppc_stub_type): Add ppc_stub_global_entry.
	(struct ppc_link_hash_table): Increase size of stub_count array.
	(build_global_entry_stubs): Emit symbol on global entry stub.
	(ppc64_elf_build_stubs): NULL check htab->brlt.  Add global entry
	stub stats.
ld/
	* emultempl/ppc64elf.em (stub_added): Delete.
	(gld${EMULATION_NAME}_finish): Call ppc64_elf_build_stubs even when
	none of the usual stubs have been added.  Only change entry_section
	for ELFv1.