gettime: silence sanitizer overflow warning

A warning is triggered in clang's unsigned integer sanitizer while two
seq values are subtracted from each other during the clock_cmp qsort
comparator:

gettime.c:657:17: runtime error: unsigned integer overflow: 2 - 3 cannot be represented in type 'unsigned int'

While pedantically correct, the issue is harmless since the result is
ultimately cast into a (signed) int on the function's return thus it
will be interpreted correctly within qsort. However it's easy to silence
the warning by changing clock_entry.seq from a uint32_t to a int32_t so
even though we've reduced the range we hopefully make it easier to see
and diagnose real overflow issues sooner in the future.

Signed-off-by: Sitsofe Wheeler <sitsofe@yahoo.com>

gettime.c

@@ -554,7 +554,7 @@ uint64_t time_since_now(const struct timespec *s)
 #define CLOCK_ENTRIES_TEST	1000
 
 struct clock_entry {
-	uint32_t seq;
+	int32_t seq;
 	uint32_t cpu;
 	uint64_t tsc;
 };