Build trivial_example by default.

Add doc/trivial_example.c to the autotools build so we get
some minimal verification that the code compiles.

Signed-off-by: Mark Harris <mark.hsj@gmail.com>
2 jobs for trivial in 4 minutes and 48 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #10248
docker
autoconf

00:04:48

passed #10249
docker
cmake

00:00:51