Fix build failure of Ada runtime for Aarch64 targets

Fix build failure of Ada runtime for Aarch64 targets

The Aarch64 back-end now asserts that the main variant of scalar types
has TYPE_USER_ALIGN cleared, and that's not the case for scalar types
declared with a confirming alignment clause in Ada.

gcc/ada/
	PR bootstrap/109510
	* gcc-interface/decl.cc (gnat_to_gnu_entity) <types>: Reset align
	to zero if its value is equal to TYPE_ALIGN and the type is scalar.
	Set TYPE_USER_ALIGN on the type only if align is positive.