[Threading] Always round up when converting std::chrono::durations.

We were inadvertently rounding down, which was fine almost 100% of the
time, but on Windows where the timer resolution is only 1ms, it made
the test _very slightly_ flaky because we were asking to wait for
9ms rather than 10ms, then checking we'd waited at least 10ms.

We should explicitly round up, for that reason.

rdar://100236038

include/swift/Threading/Impl/Pthreads.h

@@ -21,9 +21,10 @@
 #include <pthread.h>
 
 #include <atomic>
-#include <chrono>
 #include <cstdint>
 
+#include "chrono.h"
+
 #include "llvm/ADT/Optional.h"
 
 #include "swift/Threading/Errors.h"
@@ -163,14 +164,14 @@ inline void cond_wait(cond_handle &handle) {
 template <class Rep, class Period>
 inline bool cond_wait(cond_handle &handle,
                       std::chrono::duration<Rep, Period> duration) {
-  auto deadline = std::chrono::time_point_cast<
-    std::chrono::system_clock::duration>(std::chrono::system_clock::now()
-                                         + duration);
+  auto to_wait = chrono_utils::ceil<
+    std::chrono::system_clock::duration>(duration);
+  auto deadline = std::chrono::system_clock::now() + to_wait;
   return cond_wait(handle, deadline);
 }
 inline bool cond_wait(cond_handle &handle,
                       std::chrono::system_clock::time_point deadline) {
-  auto ns = std::chrono::duration_cast<std::chrono::nanoseconds>(
+  auto ns = chrono_utils::ceil<std::chrono::nanoseconds>(
     deadline.time_since_epoch()).count();
   struct ::timespec ts = { ::time_t(ns / 1000000000), long(ns % 1000000000) };
   SWIFT_PTHREADS_RETURN_TRUE_OR_FALSE(