abcl:  Fix the ABCL function pointers for jna-4.0.0.

The special variable *JNA-STRING-ENCODING* now contains the parameter
used in the underlying Java constructor for function pointers that
specifies the encoding between Java and native strings.  Usage of CFFI
with jna-3.5.1 or earlier ignores this variable.
cffi-ecl: export %CLOSE-FOREIGN-LIBRARY

Reported by Philipp Marek.