.Install PHP as a Module
In PHP src directory (php_4.2.3)
# ./configure --with-mysql \
--with-apxs=/usr/local/apache/bin/apxs

[root@li10-60 php-4.3.10]# ./configure --with-mysql --with-apxs=/usr/local/apache/bin/apxs
loading cache ./config.cache
checking host system type... i686-pc-linux-gnu
checking for gcc... gcc
checking whether the C compiler (gcc ) works... yes
checking whether the C compiler (gcc ) is a cross-compiler... no
checking whether we are using GNU C... yes
checking whether gcc accepts -g... yes
checking whether gcc and cc understand -c and -o together... yes
checking how to run the C preprocessor... gcc -E
checking for AIX... no
checking if compiler supports -R... no
checking if compiler supports -Wl,-rpath,... yes
checking for re2c... exit 0;
checking for ranlib... ranlib
checking whether ln -s works... yes
checking for mawk... no
checking for gawk... gawk
checking for bison... no
checking for byacc... no
configure: warning: You will need bison if you want to regenerate the PHP parsers.
checking for flex... lex
checking for yywrap in -ll... no
checking lex output file root... ./configure: line 2425: lex: command not found
configure: error: cannot find output from lex; giving up
[root@li10-60 php-4.3.10]#

[root@li10-60 php-4.3.10]# ./configure --with-mysql --with-apxs=/usr/local/apache/bin/apxs
loading cache ./config.cache
checking host system type... i686-pc-linux-gnu
checking for gcc... gcc
checking whether the C compiler (gcc ) works... yes
checking whether the C compiler (gcc ) is a cross-compiler... no
checking whether we are using GNU C... yes
checking whether gcc accepts -g... yes
checking whether gcc and cc understand -c and -o together... yes
checking how to run the C preprocessor... gcc -E
checking for AIX... no
checking if compiler supports -R... no
checking if compiler supports -Wl,-rpath,... yes
checking for re2c... exit 0;
checking for ranlib... ranlib
checking whether ln -s works... yes
checking for mawk... no
checking for gawk... gawk
checking for bison... no
checking for byacc... no
configure: warning: You will need bison if you want to regenerate the PHP parsers.
checking for flex... flex
checking for yywrap in -lfl... yes
checking lex output file root... lex.yy
checking whether yytext is a pointer... yes
checking for working const... yes
checking flex version... 2.5.4 (ok)
checking for pthreads_cflags... -pthread
checking for pthreads_lib...

Configuring SAPI modules
checking for AOLserver support... no
checking for Apache 1.x module support via DSO through APXS...

Sorry, I was not able to successfully run APXS. Possible reasons:

1. Perl is not installed;
2. Apache was not compiled with DSO support (--enable-module=so);
3. 'apxs' is not in your path. Try to use --with-apxs=/path/to/apxs
The output of /usr/local/apache/bin/apxs follows
./configure: line 3169: /usr/local/apache/bin/apxs: No such file or directory
configure: error: Aborting
[root@li10-60 php-4.3.10]#