This patch makes GNAT.Array_Split a preelaborable unit. As a result, it can be
withed by other preelaborated untis.

2018-06-11  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* libgnat/g-arrspl.ads: Add pragma Preelaborate.

gcc/testsuite/

	* gnat.dg/gnat_array_split1.adb, gnat.dg/gnat_array_split1.ads: New
	testcase.

From-SVN: r261419