In DCE 1.1, the time_low value is defined as an unsigned 32-bit

In DCE 1.1, the time_low value is defined as an unsigned 32-bit
integer.  Presently, our implementation employs an approach that
converts the value to int64_t, then back to int, unfortunately,
this approach can be problematic when the the difference between
the two time_low is larger than 0x7fffffff, as the value is then
truncated to int.

To quote the test case from the original PR, the following is
true with the current implementation:

865e1a56-b9d9-11d9-ba27-0003476f2e88 < 062ac45c-b9d9-11d9-ba27-0003476f2e88

However, according to the DCE specification, the expected result
should be:

865e1a56-b9d9-11d9-ba27-0003476f2e88 > 062ac45c-b9d9-11d9-ba27-0003476f2e88

This commit adds a new intermediate variable which uses int64_t
to store the result of subtraction between the two time_low values,
which would not introduce different semantic of the MSB found in
time_low value.

PR:		83107
Submitted by:	Steve Sears <sjs at acm dot org>
MFC After:	1 month