re PR tree-optimization/23911 (Failure to propagate constants from a const initializer for _Complex)

gcc/
	PR tree-optimization/23911
	* tree-ssa-ccp.c (fold_const_aggregate_ref): Handle REALPART_EXPR
	and IMAGPART_EXPR too.

testsuite/
	* gcc.dg/pr23911.c: New test.

From-SVN: r104771