PR23850, strip should not discard/move .rela.plt in executable

PR23850, strip should not discard/move .rela.plt in executable

strip/objcopy can't deal with alloc reloc sections, not .rela.dyn or
.rela.plt in a dynamic executable, or .rela.plt/.rela.iplt in a static
executable.  So, don't have BFD treat them as side-channel data
associated with the section they are relocating.

	PR 23850
	* elf.c (bfd_section_from_shdr): Treat SHF_ALLOC SHT_REL* sections
	in an executable or shared library as normal sections.