I installed apache 2.0.45 from source, then clsdk 2.81 (the most recent version available). 

then I set up informixdir, and I launch:

./configure --with-apxs2=/usr/sbin/apxs --with-informix=yes

then I launch make, and I see:

Incorrectly built binary which accesses errno, h_errno or _res directly. Needs to be fixed.
/bin/sh libtool --silent --mode=compile gcc -I/u/informix/incl/esql -Iext/informix/ -I/root/updates/php-4.3.1/ext/informix/ -DPHP_ATOM_INC -I/root/updates/php-4.3.1/include -I/root/updates/php-4.3.1/main -I/root/updates/php-4.3.1 -I/usr/include/apache -I/root/updates/php-4.3.1/Zend -I/root/updates/php-4.3.1/ext/xml/expat  -I/root/updates/php-4.3.1/TSRM  -g -O2  -prefer-pic -c /root/updates/php-4.3.1/ext/informix/ifx.c -o ext/informix/ifx.lo
/root/updates/php-4.3.1/ext/informix/ifx.ec: In function `zm_info_ifx':
/root/updates/php-4.3.1/ext/informix/ifx.ec:387: parse error before '/' token
/root/updates/php-4.3.1/ext/informix/ifx.ec:3121:17: operator '<' has no left operand
make: *** [ext/informix/ifx.lo] Error 1

I try to edit the file /root/updates/php-4.3.1/ext/informix/ifx.ec
and I put in some /* and */ to comment out some lines (one if and one endif, lines 3121 and 3134


make again...
and I get:
/root/updates/php-4.3.1/ext/informix/ifx.ec:387: parse error before '/' token

the line was:

sprintf(buf, "%02.2f", (double)(IFX_VERSION/100.0));
 I modify in: 
sprintf(buf, "%02.2f", (double)(100.0));

then I launch make again...

and I get:

ext/mysql/libmysql/my_tempnam.lo(.text+0x4c): In function `my_tempnam':
/root/updates/php-4.3.1/ext/mysql/libmysql/my_tempnam.c:103: the use of `tempnam' is dangerous, better use `mkstemp'
ext/mysql/libmysql/my_lib.lo(.text+0x3d1): In function `my_dir':
/root/updates/php-4.3.1/ext/mysql/libmysql/my_lib.c:169: undefined reference to
`errno'
ext/mysql/libmysql/my_lib.lo(.text+0x5ef): In function `my_stat':
/root/updates/php-4.3.1/ext/mysql/libmysql/my_lib.c:588: undefined reference to
`errno'
ext/mysql/libmysql/my_malloc.lo(.text+0xde): In function `my_malloc':
/root/updates/php-4.3.1/ext/mysql/libmysql/my_malloc.c:24: undefined reference to `errno'
ext/mysql/libmysql/my_realloc.lo(.text+0xd5): In function `my_realloc':
/root/updates/php-4.3.1/ext/mysql/libmysql/my_realloc.c:44: undefined reference
to `errno'
ext/mysql/libmysql/my_delete.lo(.text+0x86): In function `my_delete':
/root/updates/php-4.3.1/ext/mysql/libmysql/my_delete.c:16: undefined reference to `errno'
ext/mysql/libmysql/my_tempnam.lo(.text+0x89):/root/updates/php-4.3.1/ext/mysql/libmysql/my_tempnam.c:108: more undefined references to `errno' follow
/u/informix/lib/esql/libifgls.so: undefined reference to `__ctype_b'
/u/informix/lib/esql/libifgls.so: undefined reference to `__ctype_toupper'
/u/informix/lib/esql/libifgls.so: undefined reference to `__ctype_tolower'
collect2: ld returned 1 exit status
make: *** [sapi/cli/php] Error 1

MYSQL??? why? I don't want it, i did not wrote --with-mysql!!!

I am quite lost: I managed to install PHP 4.2.3 (and with the same "workarounds" explained before, it worked...) but I wish to install 4.3.1!

Any Ideas?