time: use GetSystemTimePreceiseAsFileTime on Windows

Use the `GetSystemTimePreciseAsFileTime` rather than
`GetSystemTimeAsFileTime` as we may otherwise get a cached value from
the last context switch.

Author: compnerd

src/shims/time.h

@@ -112,7 +112,7 @@ _dispatch_get_nanoseconds(void)
 	// FILETIME is 100-nanosecond intervals since January 1, 1601 (UTC).
 	FILETIME ft;
 	ULARGE_INTEGER li;
-	GetSystemTimeAsFileTime(&ft);
+	GetSystemTimePreciseAsFileTime(&ft);
 	li.LowPart = ft.dwLowDateTime;
 	li.HighPart = ft.dwHighDateTime;
 	return li.QuadPart * 100ull - kNTToUNIXBiasAdjustment;