Check return status of memory alloc functions

Check return status of memory alloc functions

This fixes a number of places that call a memory allocation function
without checking for a NULL return before using.

	* mach-o.c (bfd_mach_o_flatten_sections): Return a bfd_boolean,
	FALSE if memory alloc fails.  Adjust calls.
	* som.c (som_prep_for_fixups): Likewise.
	* vms-alpha.c (alpha_vms_add_fixup_lp, alpha_vms_add_fixup_ca),
	(alpha_vms_add_fixup_qr, alpha_vms_add_fixup_lr),
	(alpha_vms_add_lw_reloc, alpha_vms_add_qw_reloc): Likewise.
	* som.c (som_build_and_write_symbol_table): Return via error_return
	on seek failure.
	* vms-alpha.c (VEC_APPEND): Adjust for vector_grow1 changes.
	(VEC_APPEND_EL): Delete.
	(vector_grow1): Return pointer to element.  Catch overflow.
	Return NULL on memory allocation failure.
	(alpha_vms_add_fixup_lp): Replace VEC_APPEND_EL with VEC_APPEND.
	(alpha_vms_add_fixup_ca): Likewise.
	(alpha_vms_link_add_object_symbols): Check VEC_APPEND result
	before using.
	* elf.c (bfd_section_from_shdr): Check bfd_zalloc2 result.