PowerPC64 pcrel got relocs against local symbols

Not that anyone would want to indirect via the GOT when an address can
be loaded directly with pla, the following:

 pld 3,x@got@pcrel
x:

leads to "Internal error in md_apply_fix", because the generic parts
of assembler fixup handling convert the fx_pcrel fixup to one without
a symbol.  Stop that happening.

	* config/tc-ppc.c (ppc_force_relocation): Add PLT_PCREL34 and
	assorted GOT_PCREL34 relocs.

(cherry picked from commit 49c3ed08)