gitlab-ci: Add a basic build description.

Specify a basic autotools build so we get some feedback on changes
to gitlab-hosted repositories.

Note that the code currently doesn't build on recent distros.
1 job for gitlab-ci in 24 seconds (queued for 9 minutes and 26 seconds)
Status Job ID Name Coverage
  Build
failed #10954
docker
autotools

00:00:24

 
Name Stage Failure
failed
autotools Build
  385 |     _nc_init_acs();
| ^~~~~~~~~~~~
In file included from mincurses.c:40:
/usr/include/term_entry.h:225:29: note: declared here
225 | extern NCURSES_EXPORT(void) _nc_init_acs (void) NCURSES_TACK_1_08; /* corresponds to traditional 'init_acs()' */
| ^~~~~~~~~~~~
make: *** [Makefile:424: mincurses.o] Error 1
Cleaning up file based variables
ERROR: Job failed: exit code 1