Configure misidentifies clock_gettime and getentropy on macOS Sierra/XCode8 when compiling for iOS 8
libSystem.dylib provides clock_gettime and getentropy from iOS 10 onward but not below but the configure script does not detect that. Even with the
linker flag. The only way I managed to compile for iOS8 and iOS9 on macOS Sierra with XCode8 was to patch out detection of clock_gettime and getentropy from the configure script. This is less-than-ideal but the only fix I know. I attached the patch that I used on configure.