It is located right at the top of the module source:
To build: apxs2 -i -c mod_proxy_uwsgi.c
Apxs2 is specific to Apache-2.2, and it can be called apxs on some Unix. For example, on CentOS 6:
$ rpm -q -f `which apxs` httpd-devel-2.2.15-28.el6.centos.x86_64
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