[krbdev.mit.edu #3434] sizeof type should be checked at compile time, not configure time

[Ken Raeburn via RT]

Mac fat binaries get built with one command invocation, for multiple
architectures.  I think we're okay on endianness, but the gssapi code,
at least, uses some configure-time tests to determine type sizes and
thus choose the "right" 32-bit type.

I think we'll probably win on the Mac 64-bit platforms just because we
happen to do the tests in the right order, and int is probably right on
all of them, but it would be better if we tested the max-value macros
from  the system headers, and got rid of the configure-time tests.