expmed.c (extract_bit_field): Update function comment regarding alt_rtl.

2019-09-09  Bernd Edlinger  <bernd.edlinger@hotmail.de>

        * expmed.c (extract_bit_field): Update function comment
        regarding alt_rtl.
        * expr.c (expand_expr_real): Update function comment
        regarding alt_rtl.
        (expand_misaligned_mem_ref): New helper function.
        (expand_expr_real_2): Use expand_misaligned_mem_ref.
        Remove duplicate assignment to "base" at case MEM_REF.
        Remove a shadowed variable "unsignedp" at case VCE.

From-SVN: r275541