It's right at the top of the module's source:
To build:
apxs2 -i -c mod_proxy_uwsgi.c
Apxs2 is apache-2.2 specific, and it may be called apxs on some Unixes. For instance, on CentOS 6:
$ rpm -q -f `which apxs`
httpd-devel-2.2.15-28.el6.centos.x86_64