Using -host option in setup scripts is incorrect

[felix winkelmann]

Using the -host option in setup scripts will not work as intended: the import library for a cross-compiled extension still needs to be target-specific, as it will be used when the extension is loaded into the interpreter. A cross-compiled extension should be simply be also installed for the cross chicken (here we do need -host' mode, but for chicken-install, not csc` directly).