* print-rtl.c (print_rtx): Display the real-value equivalent of
        a const_double when easy.
        * real.h (REAL_VALUE_TO_TARGET_SINGLE): Use a union to pun types.
        Zero memory first for predictability.
        (REAL_VALUE_TO_TARGET_DOUBLE): Likewise.
        * varasm.c (immed_real_const_1): Notice width of H_W_I == double.

From-SVN: r20972