build script: automatically detect installed SDK version

Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>

compileVLCforiOS.sh

@@ -5,7 +5,7 @@
 set -e
 
 PLATFORM=iphoneos
-SDK=7.1
+SDK=`xcrun --sdk iphoneos --show-sdk-version`
 SDK_MIN=6.1
 VERBOSE=no
 CONFIGURATION="Release"