Can't build for iOS Simulator

[PeteClubSeven]

Hi,

I'm not sure whether this is desired or not but I noticed that tools/build_ios.sh supports PLATFORM_NAME=iphonesimulator. Unfortunately when I try to compile with this I end up running into linker errors with my application. The error is as follows:

ld: building for 'iOS-simulator', but linking in dylib ([...]/cktap-protocol-flutter/contrib/tap-protocol/build/libtap-protocol.dylib) built for 'iOS'

I tried modifying the CMakeLists.txt to use the correct libsecp256k1.a when building for the iOS-simulator but it doesn't fix the core issue.

For my use case I will test if there's a way I can work around this by excluding my plugin from building when targeting an iOS simulator. Feel free to close this if you don't wish to support the simulator.

[PeteClubSeven]

Since #13 this may be solved however I don't have time to revisit the issue right now.