Make fixes and improvements

- Introduce __assert_disable global
- Improve strsignal() thread safety
- Make system call tracing thread safe
- Fix SO_RCVTIMEO / SO_SNDTIMEO on Windows
- Refactor DescribeFoo() functions into one place
- Fix fork() on Windows when TLS and MAP_STACK exist
- Round upwards in setsockopt(SO_RCVTIMEO) on Windows
- Disable futexes on OpenBSD which seem extremely broken
- Implement a better kludge for monotonic time on Windows

libc/calls/now.c

@@ -16,6 +16,7 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/assert.h"
 #include "libc/bits/bits.h"
 #include "libc/bits/initializer.internal.h"
 #include "libc/bits/safemacros.internal.h"
@@ -44,10 +45,10 @@ static long double GetTimeSample(void) {
   uint64_t tick1, tick2;
   long double time1, time2;
   sched_yield();
-  time1 = dtime(CLOCK_MONOTONIC_FAST);
+  time1 = dtime(CLOCK_REALTIME_FAST);
   tick1 = rdtsc();
   nanosleep(&(struct timespec){0, 1000000}, NULL);
-  time2 = dtime(CLOCK_MONOTONIC_FAST);
+  time2 = dtime(CLOCK_REALTIME_FAST);
   tick2 = rdtsc();
   return (time2 - time1) * 1e9 / MAX(1, tick2 - tick1);
 }
@@ -75,13 +76,13 @@ static long double MeasureNanosPerCycle(void) {
 void RefreshTime(void) {
   struct Now now;
   now.cpn = MeasureNanosPerCycle();
-  now.r0 = dtime(CLOCK_REALTIME);
+  now.r0 = dtime(CLOCK_REALTIME_FAST);
   now.k0 = rdtsc();
   memcpy(&g_now, &now, sizeof(now));
 }
 
 static long double nowl_sys(void) {
-  return dtime(CLOCK_REALTIME);
+  return dtime(CLOCK_REALTIME_FAST);
 }
 
 static long double nowl_art(void) {
@@ -92,7 +93,8 @@ static long double nowl_art(void) {
 static long double nowl_vdso(void) {
   long double secs;
   struct timespec tv;
-  __gettime(CLOCK_REALTIME, &tv);
+  assert(__gettime);
+  __gettime(CLOCK_REALTIME_FAST, &tv);
   secs = tv.tv_nsec;
   secs *= 1 / 1e9L;
   secs += tv.tv_sec;