In src/libkeymap/keymap/common.h there is a func prototype int lk_set_log_fn(...) which includes a va_list in the parameters, but the header does not include <stdarg.h>. This works on glibc systems because of the way the header stack but not on uclibc or other libc's. (man va_start for more info.)
Simple fix, just #include <stdarg.h> somewhere near the top. This should go upstream.
should be all set now in the tree; thanks for the report!
Commit message: Add missing stdarg.h include to fix building for some C libraries