bash$ shopt -s globstar
bash$ wc **/*.c
Somewhat sadly, the Glibc glob function does not have an equivalent GLOB_ option for this; it's just in Bash.
-bash: shopt: globstar: invalid shell option name
In the git repo, there is a 2009-dated commit 3185942a5234e26ab13fa02f9c51d340cec514f8 where the material appears, as a snapshot import.
Make sure you're using "shopt -s globstar" and not "shopt -o globstar".