(split) Move KDTRACE_FRAME to "options" since it's used by kern.pre.mk.
(split) Fix undefined behavior: (1 << 31) is not defined as 1 is an int and this
shifts into the sign bit.  Instead use (1U << 31) which gets the
expected result.

This fix is not ideal as it assumes a 32 bit int, but does fix the issue
for most cases.

A similar change was made in OpenBSD.

Discussed with:	-arch, rdivacky
Reviewed by:	cperciva
(split) Merge branch 'CURRENT' (commit '36d4a7a0')