Fix bad interaction between --relax and tls optimisation

Fix bad interaction between --relax and tls optimisation

Adding long-branch stubs for __tls_get_addr calls that are optimised
away is silly.  It also causes assertion failures on newer object files
that use R_PPC_TLSGD and R_PPC_TLSLD marker relocs, and half-optimised
(ie. broken) code for older object files.

	PR 16546
	* elf32-ppc.c (ppc_elf_relax_section): Don't build long-branch
	stubs for calls to __tls_get_addr that we know will later be
	optimised away.