Add HOSTING_SCRT0 for PIE test

ld/

	* Makefile.am (HOSTING_SCRT0): New.

	* configure.host (HOSTING_SCRT0): New.  Used for PIE.

	* configure.in (HOSTING_SCRT0): New AC_SUBST.

	* Makefile.in: Regenerated.
	* configure: Likewise.

ld/testsuite/

	* config/default.exp (get_target_emul): Also set HOSTING_SCRT0.

	* lib/ld-lib.exp (default_ld_link): Use HOSTING_SCRT0 for -pie.