Build warnings

[borud]

Compiling produces the following warnings.

_cgo_main.c:2:23: warning: unused parameter 'fn' [-Wunused-parameter]
_cgo_main.c:2:61: warning: unused parameter 'a' [-Wunused-parameter]
_cgo_main.c:2:68: warning: unused parameter 'c' [-Wunused-parameter]
_cgo_main.c:2:85: warning: unused parameter 'ctxt' [-Wunused-parameter]
_cgo_main.c:4:41: warning: unused parameter 'ctxt' [-Wunused-parameter]
_cgo_main.c:6:26: warning: unused parameter 'a' [-Wunused-parameter]
_cgo_main.c:6:33: warning: unused parameter 'c' [-Wunused-parameter]
_cgo_main.c:7:23: warning: unused parameter 'a' [-Wunused-parameter]
_cgo_main.c:7:30: warning: unused parameter 'c' [-Wunused-parameter]