Add Linux support for core:time

In addition to sleep() and now(), it also defines nanosleep(), boot_time() and seconds_since_boot()

core/time/time_linux.odin

@@ -0,0 +1,44 @@
+package time
+
+import "core:os";
+import "core:fmt";
+
+// NOTE(Jeroen): The times returned are in UTC
+
+now :: proc() -> Time {
+
+    time_spec_now := os.clock_gettime(os.CLOCK_REALTIME);
+    ns := time_spec_now.tv_sec * 1e9 + time_spec_now.tv_nsec;
+    return Time{_nsec=ns};
+}
+
+boot_time :: proc() -> Time {
+
+    ts_now := os.clock_gettime(os.CLOCK_REALTIME);
+    ts_boottime := os.clock_gettime(os.CLOCK_BOOTTIME);
+
+    ns := (ts_now.tv_sec - ts_boottime.tv_sec) * 1e9 + ts_now.tv_nsec - ts_boottime.tv_nsec;
+    return Time{_nsec=ns};
+}
+
+seconds_since_boot :: proc() -> f64 {
+
+    ts_boottime := os.clock_gettime(os.CLOCK_BOOTTIME);
+    return f64(ts_boottime.tv_sec) + f64(ts_boottime.tv_nsec) / 1e9;
+}
+
+sleep :: proc(d: Duration) {
+
+    ds := duration_seconds(d);
+    seconds := u64(ds);
+    nanoseconds := i64((ds - f64(seconds)) * 1e9);
+
+    if seconds > 0 do os.sleep(seconds);
+    if nanoseconds > 0 do os.nanosleep(nanoseconds);
+}
+
+nanosleep :: proc(d: Duration) {
+    // NOTE(Jeroen): os.nanosleep returns -1 on failure, 0 on success
+    // duration needs to be [0, 999999999] nanoseconds.
+    os.nanosleep(i64(d));
+}