(common_type): Use TYPE_MAIN_VARIANT when preferring

(common_type): Use TYPE_MAIN_VARIANT when preferring
long int to int (when width is the same).

(check_format): With -Wformat, warn about
printf("%ld", 1) even if sizeof (int) == sizeof (long),
since the code isn't portable.  Similarly for "%d" vs 1L.

(convert_arguments) [PROMOTE_PROTOTYPES]:
With -Wconversion, use unpromoted type to check for signedness changes.

From-SVN: r4935