Issue description：
[*] make ios toolchain ffmpeg-armv7
[*] configurate ffmpeg
[*] check OpenSSL
[*] configure
xcrun -sdk iphoneos clang is unable to create an executable file.
C compiler test failed.
---------------Solution:
First
1)check your Git version
2)make sure you are using the lastest version from Git
Second
1)find "ffmpeg-armv7/ffbuild/config.log" search the detail error with keyword like "xcrun: error"
2)my case ,found the detail "xcrun: error: SDK "iphoneos" cannot be located"
Third
1)terminal input "sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer/"
2)input password
3)try again