Add CONST1_RTX (vector mode) support.

Add CONST1_RTX (vector mode) support.

* emit-rtl.c (gen_const_vector): Renamed from gen_const_vector_0.
Add integer argument named constant.  Use const_tiny_rtx instead of
CONST0_RTX.
(gen_rtx_CONST_VECTOR): Rewrite to handle checks for both CONST0_RTX
and CONST1_RTX.
(init_emit_once): Fix users of gen_const_vector.  Set CONST1_RTX for
vector types.
* expr.c (const_vector_from_tree): Call gen_rtx_CONST_VECTOR instead
of gen_rtx_raw_CONST_VECTOR.

From-SVN: r87337