[stdlib] Buildfix OpenBSD by adding clock types. (#41857)

Reading SE-0329 and this module, two clock types are broadly defined,
"continuous", which advances during suspension, and "suspending", which
does not.

SE-0329 notes the behavior of the clock types on "Darwin and BSD" is
that `CLOCK_MONOTONIC` is "continuous" and `CLOCK_UPTIME` is
"suspending". This is also true for OpenBSD (see
https://man.openbsd.org/clock_gettime).

Update code to match. This buildfixes this platform.

Author: 3405691582

stdlib/public/Concurrency/Clock.cpp

@@ -37,7 +37,7 @@ void swift_get_time(
       clock_gettime(CLOCK_BOOTTIME, &continuous);
       *seconds = continuous.tv_sec;
       *nanoseconds = continuous.tv_nsec;
-#elif defined(__APPLE__) && HAS_TIME
+#elif (defined(__APPLE__) || defined(__OpenBSD__)) && HAS_TIME
       struct timespec continuous;
       clock_gettime(CLOCK_MONOTONIC, &continuous);
       *seconds = continuous.tv_sec;
@@ -71,6 +71,11 @@ void swift_get_time(
       clock_gettime(CLOCK_UPTIME_RAW, &suspending);
       *seconds = suspending.tv_sec;
       *nanoseconds = suspending.tv_nsec;
+#elif defined(__OpenBSD__) && HAS_TIME
+      struct timespec suspending;
+      clock_gettime(CLOCK_UPTIME, &suspending);
+      *seconds = suspending.tv_sec;
+      *nanoseconds = suspending.tv_nsec;
 #elif defined(_WIN32)
       LARGE_INTEGER freq;
       QueryPerformanceFrequency(&freq);
@@ -106,7 +111,7 @@ switch (clock_id) {
       clock_getres(CLOCK_BOOTTIME, &continuous);
       *seconds = continuous.tv_sec;
       *nanoseconds = continuous.tv_nsec;
-#elif defined(__APPLE__) && HAS_TIME
+#elif (defined(__APPLE__) || defined(__OpenBSD__)) && HAS_TIME
       struct timespec continuous;
       clock_getres(CLOCK_MONOTONIC, &continuous);
       *seconds = continuous.tv_sec;
@@ -129,6 +134,10 @@ switch (clock_id) {
       clock_getres(CLOCK_UPTIME_RAW, &suspending);
       *seconds = suspending.tv_sec;
       *nanoseconds = suspending.tv_nsec;
+#elif defined(__OpenBSD__) && HAS_TIME
+      clock_getres(CLOCK_UPTIME, &suspending);
+      *seconds = suspending.tv_sec;
+      *nanoseconds = suspending.tv_nsec;
 #elif defined(_WIN32)
       *seconds = 0;
       *nanoseconds = 1000;