re PR bootstrap/59934 (Bootstrap fail since r206941: expmed.h:252:33: error: array subscript is above array bounds)

       PR bootstrap/59934
        * expmed.h (expmed_mode_index): Rework so that analysis and optimziers
        know when the MODE_PARTIAL_INT and MODE_VECTOR_INT cases can never be
        reached.

From-SVN: r207137