This is a fix for PR ld/16744 which showed that an object file linked with -r and -z [no]execstack
would not honour the [no]execstack.  Fully linked binaries use a special segment to indicate the
state of the stack, but relocatable object files only have sections, and .note.GNU-stack was not
being created.

	* emultempl/elf32.em (_after_open): Create a .note.GNU-stack
	section when performing a relocatable link with -z [no]execstack
	specified.