This (Invalid Apache directory – unable to find httpd.h under /usr/include/httpd/) error has been a thorn in my side while building a php rpm with the –with-apache php config argument. I’m running CentOS 6 and have the httpd-devel package installed which places the apache header files (including httpd.h) in /usr/include/httpd. Perms on the /usr/include/httpd directory are 755 and the files inside are 644. Everything looked good.
Turns out that –with-apache builds the static apache 1.x module which isn’t really what you want if you have installed apache in the last 10 years. What you want instead is –with-apxs2 which will build the apache 2.x shared library.