[Ada] Fix bogus error on array with overaligned scalar component

[Ada] Fix bogus error on array with overaligned scalar component

The compiler would wrongly reject an alignment clause larger than 8 on
the component type of an array of scalars, which is valid albeit
pathological.

2019-07-03  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* layout.adb (Layout_Type): Do not set the component size of an
	array with a scalar component if the component type is
	overaligned.

gcc/testsuite/

	* gnat.dg/alignment14.adb: New testcase.

From-SVN: r272968