PowerPC64 ELFv1 undefined weak functions

PowerPC64 ELFv1 undefined weak functions

Undefined weak functions, like __gmon_start__, were not being made
dynamic or emitting plt call code.  While the behaviour of undefined
weak symbols is not defined in the ELF standard, the intention on
powerpc64 was to make it possible to link without a definition of such
symbols and at run time behave the same as if a definition was found
at link time in a shared library.

	* elf64-ppc.c (ppc64_elf_adjust_dynamic_symbol): Don't exit with
	non_got_ref true in any case where we could have generated dynbss
	copies but decide not to do so.