Also around since 2005 is this function

Author: NattyNarwhal

config.m4

@@ -83,10 +83,7 @@ if test "$PHP_PDO_IBM" != "no"; then
     PHP_NEW_EXTENSION(pdo_ibm, $php_pdo_ibm_sources_core, $ext_shared,,-I$pdo_cv_inc_path)
   fi
 
-  ifdef([PHP_ADD_EXTENSION_DEP],
-  [
-    PHP_ADD_EXTENSION_DEP(pdo_ibm, pdo)
-  ])
+  PHP_ADD_EXTENSION_DEP(pdo_ibm, pdo)
 
   PHP_SUBST(PDO_IBM_SHARED_LIBADD)