MFC 244776, 244792:

MFC 244776, 244792:

gcc: avoid generating negative values to DW_AT_byte_size.

There is a bug in gcc (GCC/35998) where dwarf reports
sizes of unsigned -1 (0xffffffff).

On NetBSD this generated a faulty CTF entry which then
caused a segfault in ctfmerge. The issue was worked
around in NetBSD's Dtrace but since the issue originated
in gcc, it seems reasonable to fix it here.

Thanks to Christoph Mallon for pointing out a correct fix.

git-svn-id: svn://svn.freebsd.org/base/stable/8@245024 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f