Introduce fast path for the widely used marker operation.

Introduce fast path for the widely used marker operation.
* alloc.c (build_marker): New function.
* lisp.h (build_marker): New prototype.
* buffer.c (clone_per_buffer_values, Fmake_indirect_buffer): Use it.
* composite.c (autocmp_chars): Likewise.
* editfns.c (buildmark): Remove.
(Fpoint_marker, Fpoint_min_marker, Fpoint_max_marker)
(save_restriction_save): Use build_marker.
* marker.c (buf_charpos_to_bytepos, buf_bytepos_to_charpos): Likewise.
* window.c (save_window_save): Likewise.