[Ada] Suppress the expansion of ignored assertion pragmas

[Ada] Suppress the expansion of ignored assertion pragmas

This patch suppresses the expansion of ignored assertion pragmas.

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

gcc/ada/

	* contracts.adb (Process_Body_Postconditions): Expand only checked
	postconditions.
	(Process_Contract_Cases_For): Expand only checked contract cases.
	(Process_Inherited_Preconditions): Ignored class-wide preconditions are
	partially expanded because some of their semantic checks are tied to
	the expansion.
	(Process_Preconditions_For): Expand only checked preconditions.
	(Process_Spec_Postconditions): Expand only checked preconditions.
	Ignored class-wide preconditions are partially expanded because some of
	their semantic checks are tied to the expansion.
	* exp_prag.adb (Expand_N_Pragma): Suppress the expansion of ignored
	assertion pragmas.
	* exp_util.adb (Add_Inherited_Invariants): Code clean up.
	* sem_util.adb (Propagate_Invariant_Attributes): Code clean up.

gcc/testsuite/

	* gnat.dg/assertion_policy1.adb, gnat.dg/assertion_policy1_pkg.adb,
	gnat.dg/assertion_policy1_pkg.ads: New testcase.

From-SVN: r261430