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.

gcc/ada/adaint.c

@@ -237,6 +237,11 @@ UINT __gnat_current_ccs_encoding;
 
 #include "adaint.h"
 
+#if defined (__APPLE__) && defined (st_mtime)
+#define st_atim st_atimespec
+#define st_mtim st_mtimespec
+#endif
+
 /* Define symbols O_BINARY and O_TEXT as harmless zeroes if they are not
    defined in the current system. On DOS-like systems these flags control
    whether the file is opened/created in text-translation mode (CR/LF in