This is php4 goto this error following your install instructions

      -o httpd buildmark.o modules.o modules/standard/libstandard.a modules/php4/libphp4.a main/libmain.a ./os/unix/libos.a ap/libap.a regex/libregex.a  -Lmodules/php4 -L../modules/php4 -L../../modules/php4 -lmodphp4 -L/usr/src/php-4.0b2/ext/pcre/pcrelib -lpcre -L/usr/src/php-4.0b2/regex -lregex  -lgdbm     -lpam -ldl -lgd -lm -lcrypt -lnsl  -lresolv -rdynamic  -lm -lcrypt
main/libmain.a(http_main.o): In function `main':
http_main.o(.text+0x3db8): multiple definition of `main'
modules/php4/libphp4.a(cgi_main.o):/usr/src/php-4.0b2/cgi_main.c:197: first defined here
ld: Warning: size of symbol `main' changed from 1399 to 1614 in http_main.o
modules/php4/libphp4.a(mod_php4.o): In function `send_php':
mod_php4.o(.text+0x63c): undefined reference to `apache_php_module_main'
make[2]: *** [target_static] Error 1
make[2]: Leaving directory `/usr/src/apache_1.3.6/src'
make[1]: *** [build-std] Error 2
make[1]: Leaving directory `/usr/src/apache_1.3.6'
make: *** [build] Error 2
[root@fddox-wf01 apache_1.3.6]# gcc -v
Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/2.7.2.3/specs
gcc version 2.7.2.3
[root@fddox-wf01 apache_1.3.6]#