mod-gmtime:
%Y
2020
%Y
localtime == localtime
mod-gmtime-indirect:
make: Invalid time value: ${:U1593536400}}

mtime=1593536400}
parse-errors:
make: Invalid time value: -1}.

: -1 becomes mtime=-1}.
make: Invalid time value:  1}.

: space 1 becomes mtime= 1}.
: 0 becomes ok.
: 1 becomes Thu Jan  1 00:00:01 1970.
: INT32_MAX becomes Tue Jan 19 03:14:07 2038.
: INT32_MAX + 1 becomes Tue Jan 19 03:14:08 2038.
make: Invalid time value: 10000000000000000000000000000000}.

: overflow becomes mtime=10000000000000000000000000000000}.
make: Invalid time value: error}.

: letter becomes mtime=error}.
exit status 0