Currently, one cannot build this without modifying some upstream files. I believe a change occurred around 28-Dec (using packages from 27-Dec-2020 allows the current PKGBUILD to build successfully). In any case, the attached patch fixes the build issues.


Example failure without patch:
po -c -o mainloop.o mainloop.c &&\
mv -f $depbase.Tpo $depbase.Po
log.c:85:20: error: function declaration isn’t a prototype [-Werror=strict-prototypes]
85 | static const char *lxc_log_get_container_name()
| ^~~~~~~~~~~~~~~~~~~~~~~~~~
log.c: In function ‘lxc_log_get_container_name’:
log.c:85:20: error: old-style function definition [-Werror=old-style-definition]
log.c: In function ‘lxc_log_options_no_override’:
log.c:817:13: error: old-style function definition [-Werror=old-style-definition]
817 | inline void lxc_log_options_no_override()
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~