Note:
Configuration notes
You need a version of ESQL/C to compile the PHP Informix driver.
ESQL/C versions from 7.2x on should be OK. ESQL/C is now part of
the Informix Client SDK.
Make sure that the "INFORMIXDIR" variable has been set, and that
$INFORMIXDIR/bin is in your PATH before you run the "configure"
script.