macOS: Account for deployment target when checking for utimensat

The SDK for macOS 10.13 adds `utimensat`, but the symbol is not
available at runtime on older macOS versions.  Check the deployment
target before using the symbol.

Issue: cmake/cmake#17101

kwsysPlatformTestsCXX.cxx

@@ -265,6 +265,12 @@ int main()
 #ifdef TEST_KWSYS_CXX_HAS_UTIMENSAT
 #include <fcntl.h>
 #include <sys/stat.h>
+#if defined(__APPLE__)
+#include <AvailabilityMacros.h>
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 101300
+#error "utimensat not available on macOS < 10.13"
+#endif
+#endif
 int main()
 {
   struct timespec times[2] = { { 0, UTIME_OMIT }, { 0, UTIME_NOW } };