When cross-compiling, the active features do not represent target system

[felix winkelmann]

During the cross-compile, the feature-IDs for target architecture and operating system are not correct. We need to un-register those features and register features suitable for the target.

This will probably require a -no-feature option and build-variables for target architecture and platform.

The implications for this are extremely subtle, and this may be difficult to get right.

[felix winkelmann]

One possible approach would be a -no-feature ID option to disable built-in features and a make(3) variable CROSS_FEATURES that holds -[no-]feature options to be passed to csc when cross-compiling.

[felix winkelmann]

In commit f2b3bf92fb606d42f1898b8ff914cb1c352d3c32, a make-variable named TARGET_FEATURES has been given, which should contain target-specific options that will be passed to chicken by csc. This, together with the -no-feature option added in 95ed1c2d2c1ae12558d80bf7f5b5e12441729dd2 should be a start.