Can you please post the few lines output'ed from configure before this error occurs?

The -I just adds another include directory and should not be the problem.  Whats of concern is that the check for the $custom_dir/include is apparently failing, and screwing things up.

Do you have a /suitespot/include directory by chance?

Here are a few lines before/after the configure error:

checking for FastCGI support... no
checking for Zeus ISAPI support... no
checking for NSAPI support... /suitespot
checking for NSAPI include files... iPlanet/4.x style
./configure: -I/suitespot/plugins: does not exist
checking for PHTTPD support... no
checking for Pi3Web Support... no

The iPlanet NSAPI include directory is /suitespot/plugins/include

The problem is that the configure script is checking to see
if the directory "-I/suitespot/plugins" exists.
The "-I" shouldn't be included in a path check!
(the 4.2.2 configure script didn't have this bug)

   - Bob

Please try using this CVS snapshot:

  http://snaps.php.net/php4-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php4-win32-latest.zip

I think I see whats wrong. Any chance you can test out an unstable snapshot dated sometime after now.  I just put in a fix which I hope corrects this issue for you.  If it does, I'll back port it to 4.2 branch as well

This bug has been fixed in CVS.

In case this was a PHP problem, snapshots of the sources are packaged
every three hours; this change will be in the next snapshot. You can
grab the snapshot at http://snaps.php.net/.
 
In case this was a documentation problem, the fix will show up soon at
http://www.php.net/manual/.

In case this was a PHP.net website problem, the change will show
up on the PHP.net site and on the mirror sites in short time.
 
Thank you for the report, and for helping us make PHP better.

I tried compiling the latest version from CVS (200209290900),
and it still fails.
Here are a few lines from the configure output:
checking for FastCGI support... no
checking for Zeus ISAPI support... no
checking for NSAPI support... /suitespot
checking for NSAPI include files... iPlanet/4.x style
checking for /suitespot/plugins/include/nsapi.h... yes
./configure: -I/suitespot/plugins: does not exist
checking for PHTTPD support... no
checking for Pi3Web Support...

Here are the compile errors:
/bin/sh libtool --silent --mode=compile gcc  -Isapi/nsapi/ -I/home8/src/php/beta
/php4-200209290900/sapi/nsapi/ -DPHP_ATOM_INC -I/home8/src/php/beta/php4-2002092
90900/include -I/home8/src/php/beta/php4-200209290900/main -I/home8/src/php/beta
/php4-200209290900 -I/include -I/home8/src/php/beta/php4-200209290900/Zend -I/ho
me8/src/php/beta/php4-200209290900/ext/xml/expat  -D_POSIX_PTHREAD_SEMANTICS -D_
POSIX_PTHREAD_SEMANTICS -D_REENTRANT -I/home8/src/php/beta/php4-200209290900/TSR
M -DTHREAD=1  -g -O2 -pthreads -DZTS  -prefer-pic -c /home8/src/php/beta/php4-20
0209290900/sapi/nsapi/nsapi.c -o sapi/nsapi/nsapi.lo
/home8/src/php/beta/php4-200209290900/sapi/nsapi/nsapi.c:50: nsapi.h: No such fi
le or directory
/home8/src/php/beta/php4-200209290900/sapi/nsapi/nsapi.c:51: base/pblock.h: No s
uch file or directory
/home8/src/php/beta/php4-200209290900/sapi/nsapi/nsapi.c:52: base/session.h: No
such file or directory
/home8/src/php/beta/php4-200209290900/sapi/nsapi/nsapi.c:53: frame/req.h: No suc
h file or directory
/home8/src/php/beta/php4-200209290900/sapi/nsapi/nsapi.c:54: frame/protocol.h: N
o such file or directory
/home8/src/php/beta/php4-200209290900/sapi/nsapi/nsapi.c:55: base/util.h: No suc
h file or directory
/home8/src/php/beta/php4-200209290900/sapi/nsapi/nsapi.c:56: frame/log.h: No suc
h file or directory
*** Error code 1
make: Fatal error: Command failed for target `sapi/nsapi/nsapi.lo'

Thanks,
   Bob Fillmore

Here are a few lines from the new configure script:
    NSAPI_INCLUDE="$NSAPI_INC_DIR -I$NSAPI_INCLUDE"
    ...
    ep_dir="`echo $NSAPI_INCLUDE|sed 's%/*[^/][^/]*/*$%%'`"
    ep_realdir="`(cd \"$ep_dir\" && pwd)`"

Notice that ep_dir will contain the -I string,
causing the "cd" to fail.

Please try using this CVS snapshot:

  http://snaps.php.net/php4-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php4-win32-latest.zip

And as you're on solaris, make sure you're using GNU sed.

I tried snapshot php4-200209300300 and this bug is gone.
Note that I had to use GNU sed and make to get rid of
"output line too long" and other errors.
Thanks!
   - Bob