coastline should support harbours buildable only on certain architectures
Currently, the matrix script in the coastline attempts to build all harbours for all architectures. For some harbours, such as pcc, building on all architectures doesn't make sense as the harbour should be buildable only on ia32, amd64 (currently broken), ppc32, and mips32.
Each harbous should therefore have a way of expressing that it is only intended for certain archs, e.g. via a new
shiparchs variable, which would default to all archs if empty. The matrix script and also ci should take this setting into account and skip the build on the unsupported archs.