PowerPC64: remove empty .rela.dyn (.rela.branch_lt)

PowerPC64: remove empty .rela.dyn (.rela.branch_lt)

Stripping .rela.branch_lt is easy enough but messes with the
testsuite due to stub symbols (that use section id) changing.  Tests
that run on more than one target variant can be tricky to fix, this
renaming happened to work.

bfd/
	* elf64-ppc.c (ppc64_elf_size_stubs): Strip relbrlt too.
ld/
	* testsuite/ld-powerpc/tlsopt5.s: Rename foo to aaaaa.
	* testsuite/ld-powerpc/tlsopt5.d: Adjust to suit.
	* testsuite/ld-powerpc/tlsopt6.d: Likewise.