Darwin, Ada : Fix bootstrap after stat entry changes.

Darwin, Ada : Fix bootstrap after stat entry changes.

Darwin struct stat has timeval entry fields for file access and
modification times but they are named differently from those
on Linux.

As a workaround define the field names to the Darwin equivalent.

gcc/ada/ChangeLog:

	* adaint.c: On Darwin platforms, define st_atim to
	st_atimespec. Likwise st_mtim to st_mtimespec.