Error on unsupported PowerPC ifuncs

Error on unsupported PowerPC ifuncs

The pr19784 tests fail on ppc32 due to a gcc bug.  The failure should
be noticed when building both libpr19784a.so and libpr19784b.so,
rather than ld building a buggy libpr19784a.so that fails at run time.
This patch fixes that by moving the @local ifunc check out of
check_relocs, where a call destination may not yet be known to be
ifunc.  The patch also adds a related error for -mbss-plt code.

	* elf32-ppc.c (ppc_elf_check_relocs): Move error for @local ifunc..
	(ppc_elf_relocate_section): ..to here.  Comment.  Error on
	detecting -mbss-plt -fPIC local ifuncs too.
	(ppc_elf_size_dynamic_sections): Comment on unnecessary glink
	branch table entries.