title: libcurl crashes on iOS 9 when compiled with latest iOS sdk
body: <p>In iOS 10 there is <code>clock_gettime</code> function in system library.</p>
  
  <p>When i compile curl on latest iOS SDK, <code>configure</code> script always define <code>HAVE_CLOCK_GETTIME_MONOTONIC</code> (but i define <code>-miphoneos-version-min=8.0</code>!), that lead to crash on previous iOS versions. Crash looks like <code>EXC_BREAKPOINT (EXC_ARM_BREAKPOINT)</code> on <code>dylib stub_binder</code>. Crash occurred when <code>curlx_tvnow()</code> is called. With <code>HAVE_CLOCK_GETTIME_MONOTONIC</code> it calls <code>clock_gettime</code>, that is not exists on pre-iOS 10.</p>
  
  <p>Is there any way to disable <code>HAVE_CLOCK_GETTIME_MONOTONIC</code> when <code>-miphoneos-version-min</code> less then 10.0?</p>