Missing support to SHARED option

[alfredone]

Actually AmigaOS4 supports shared objects .so, but cmake doesn't allow to use SHARED option with ADD_LIBRARY, falling back to a STATIC library.

This is the warning message when using ADD_LIBRARY( SHARED ...)

CMake Warning (dev) at CMakeLists.txt:25 (ADD_LIBRARY):
ADD_LIBRARY called with SHARED option but the target platform does not
support dynamic linking. Building a STATIC library instead. This may lead
to problems.

This warning is for project developers. Use -Wno-dev to suppress it.

[MBeijer]

I didn't know this. I made the OS3 toolchain first, then replicated for the other two.

[MBeijer]

@alfredone Sorry for taking time to address this. I will look into it and bake a new docker image!