clean-temp and large files

[Eric Blake]

Is there any reason that using the clean-temp module does not AC_REQUIRE
([AC_SYS_LARGEFILE]) in the configure script?  Without that, it is possible on 
some hosts that temporary files are artificially capped at 2GiB, even though 
enabling largefile support could make things behave otherwise.  As a result, 
there is a regression in M4 1.4.8 (1.4.7 used the mkstemp module, but 1.4.8 
switched to clean-temp).

-- 
Eric Blake