[Ada] Spurious error on case expression with limited result

[Ada] Spurious error on case expression with limited result

This patch modifies the expansion of case expressions to prevent a
spurious error caused by the use of assignment statements to capture the
result of the case expression when the associated type is limited.

2019-07-10  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* exp_ch4.adb (Expand_N_Case_Expression): Mark the generated
	assignments to the temporary result as being OK because the
	expansion of case expressions is correct by construction.
	(Is_Copy_Type): Update the predicate to match the comment
	within.

gcc/testsuite/

	* gnat.dg/limited2.adb, gnat.dg/limited2_pack_1.adb,
	gnat.dg/limited2_pack_1.ads, gnat.dg/limited2_pack_2.adb,
	gnat.dg/limited2_pack_2.ads: New testcase.

From-SVN: r273336