Xcode
The Apple's default IDE is quite hostile to FPC, since it doesn't provide any source of "native" integration. In order for the compiler to be called a custom Run Script is needed to be used.
However it comes with some handy command-line tools that could be used for building projects. See Technical Note TN2339 for FAQ.
xcodebuild
List all available SDKs
xcodebuild -showsdks
Build a project by it's (project directory) name and a specified sdk
xcodebuild -sdk iphonesimulator9.1 -project testProjGen.xcodeproj
Run Script
- in order to return an error, the (bash) script must use "exit" command with non-zero value. FPC returns a non-zero value when compiling failed.
- do not specify "output files" of the script. Otherwise "Clean" will be required to make the script executed again