Non-alloc sections don't belong in PT_LOAD segments

Non-alloc sections don't belong in PT_LOAD segments

Taking them out showed a bug in the powerpc64 backend with .branch_lt
being removed from output_bfd but not from previously set up segment
section maps.  Removing the bfd sections meant their sh_flags (and
practically everything else) remaining zero, ie. not SHF_ALLOC,
triggering complaints about "`.branch_lt' can't be allocated in
segment".

include/elf/
	* internal.h (ELF_SECTION_IN_SEGMENT_1): Ensure PT_LOAD and
	similar segments only contain alloc sections.
ld/
	* emultempl/ppc64elf.em (gld${EMULATION_NAME}_after_allocation):
	Call gld${EMULATION_NAME}_map_segments regardless of need_laying_out.