Allow building on architectures that are not supported by the context
library.
Update to Chicken 4.8.0.3
Requested by Peter Bex.


Changes:

4.8.0.3

 - Runtime
    - Avoid high CPU usage when waiting for child process I/O with poll().
      Affects at least Linux and Solaris.
    - Escape single backslash in printed symbols.

 - Type system
    - Fixed types.db entry for join and mutex-lock!

 - Core tools
   - chicken-install transports now parses ports on URIs with empty paths

4.8.0.2

 - Interpreter
    - Fix regression in ,d for procedures, which resulted in an sprintf error.

 - Compiler
    - Fix rewriting of newlines (~~) in printf.

 - Runtime
    - Allow > 4GB heap on 64-bit systems (#974).
    - Added missing library (-lrt) on Solaris for nanosleep calls (#970).

 - Build system
    - Use test -f instead of test -e in identify.sh to placate Solaris.
Updated lang/chicken to 4.8.0.3