shared: Add timespec_is_zero helper

Add a helper function to check if a struct timespec is zero. This helper
will be used in the upcoming commits to transition the Weston codebase
to struct timespec.

Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

shared/timespec-util.h

@@ -29,6 +29,7 @@
 #include <stdint.h>
 #include <assert.h>
 #include <time.h>
+#include <stdbool.h>
 
 #define NSEC_PER_SEC 1000000000
 
@@ -133,6 +134,17 @@ timespec_sub_to_msec(const struct timespec *a, const struct timespec *b)
 	return timespec_sub_to_nsec(a, b) / 1000000;
 }
 
+/* Check if a timespec is zero
+ *
+ * \param a timespec
+ * \return whether the timespec is zero
+ */
+static inline bool
+timespec_is_zero(const struct timespec *a)
+{
+	return a->tv_sec == 0 && a->tv_nsec == 0;
+}
+
 /* Convert milli-Hertz to nanoseconds
  *
  * \param mhz frequency in mHz, not zero