I agree upgrading apache from prepackaged SPS is not supported.
However, if you upgrade SPS to later release R12.52sp1, you will get pre-build apache version 2.4.4
Under ~CA/secure-proxy/httpd/bin, run apachectl -V
Server version: Apache/2.4.4 (Unix)
Server built: Aug 12 2013 00:56:15
Server's Module Magic Number: 20120211:11
Server loaded: APR 1.4.8, APR-UTIL 1.5.2
Compiled using: APR 1.4.8, APR-UTIL 1.5.2
Architecture: 32-bit
...
Hongxu