ppc476 linker workaround shared lib fixes

ppc476 linker workaround shared lib fixes

When building a shared lib from non-PIC objects, we'll get dynamic
text relocations.  These need to move with any insns we move.
Otherwise the dynamic reloc will modify the branch, resulting in
crashes and other unpleasant behaviour.

Also, ld -r --ppc476-workaround used with sufficiently aligned PIC
objects needs a fix for emitted REL16 relocs.

bfd/
	* elf64-ppc.c (ppc_elf_relocate_section): Move dynamic text
	relocs with insns moved by --ppc476-workaround.  Correct
	output of REL16 relocs.
ld/testsuite/
	* ld-powerpc/ppc476-shared.s,
	* ld-powerpc/ppc476-shared.lnk,
	* ld-powerpc/ppc476-shared.d,
	* ld-powerpc/ppc476-shared2.d: New tests.
	* ld-powerpc/powerpc.exp: Run them.