[Ada] Wrong evaluation of membership test

[Ada] Wrong evaluation of membership test

The code generated by the compiler erroneously evaluates to True
membership tests when their left operand is a a class-wide interface
object and the right operand is a tagged type that implements such
interface type.

2019-07-08  Javier Miranda  <miranda@adacore.com>

gcc/ada/

	* exp_ch4.adb (Tagged_Membership): Fix regression silently
	introduced in r260738 that erroneouslusy causes the evaluation
	to True of the membership test when the left operand of the
	membership test is a class-wide interface object and the right
	operand is a type that implements such interface type.

gcc/testsuite/

	* gnat.dg/interface10.adb: New testcase.

From-SVN: r273219