Free symbol buffers if they are no longer in use

Free symbol buffers if they are no longer in use

add_specific_symbols allocates a buffer to hold symbols.  It should be
freed only if it is no longer in use.

	PR binutils/23633
	* objcopy.c (strip_specific_buffer): New.
	(strip_unneeded_buffer): Likewise.
	(keep_specific_buffer): Likewise.
	(localize_specific_buffer): Likewise.
	(globalize_specific_buffer): Likewise.
	(keepglobal_specific_buffer): Likewise.
	(weaken_specific_buffer): Likewise.
	(add_specific_symbols): Add an argument to return pointer to
	allocated buffer.
	(copy_main): Update add_specific_symbols to update pointers to
	allocated buffer.  Free pointers to allocated buffer before
	return.