simplify-rtx.c (simplify_binary_operation): Do not simplify inner elements of constant arguments of VEC_CONCAT insn.

	rtl-optimization/18614
        * simplify-rtx.c (simplify_binary_operation): Do not
        simplify inner elements of constant arguments of
        VEC_CONCAT insn.

testsuite:

        * gcc.dg/pr18614-1.c: New test.

From-SVN: r91094