iOS ccache wrapper scripts should be in the top level of the CMake build tree, so fix the output path in the configure_file().
iOS
This folder contains build configuration files for the iOS distribution of Mapbox GL Native, which ultimately targets Cocoa Touch applications written in Objective-C, Swift, or Interface Builder via the Mapbox Maps SDK for iOS. The SDK was previously developed here in this repository but is now developed in the separate mapbox-gl-native-ios repository (details).