Fix compilation on systems with empty _POSIX_TIMERS
Systems such as Tru64 ship with broken headers that
have _POSIX_TIMERS defined but empty.
CLA: trivial
@@ -76,7 +76,9 @@ static uint64_t get_timer_bits(void);
* macro that might be undefined.
*/
# undef OSSL_POSIX_TIMER_OKAY
-# if defined(_POSIX_TIMERS) && _POSIX_TIMERS > 0
+/* On some systems, _POSIX_TIMERS is defined but empty.
+ * Subtracting by 0 when comparing avoids an error in this case. */
+# if defined(_POSIX_TIMERS) && _POSIX_TIMERS -0 > 0
# if defined(__GLIBC__)
# if defined(__GLIBC_PREREQ)
# if __GLIBC_PREREQ(2, 17)
