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I get the exact same results with Version 4.2.1...
----------------------------------------------------------
# gmake install
Making install in Zend
gmake[1]: Entering directory `/Samba/holmberg/Apache/php-4.2.1/Zend'
/bin/sh ../libtool --silent --mode=compile cc -DHAVE_CONFIG_H -I. -I. -I../main 
  -I../TSRM  -O -I/usr/local/ssl/include -prefer-non-pic -static -c -o zend_oper
ators.lo `test -f zend_operators.c || echo './'`zend_operators.c
"zend_operators.c", line 566.34: 1506-275 (S) Unexpected text zval encountered.
"zend_operators.c", line 566.41: 1506-046 (S) Syntax error.
"zend_operators.c", line 566.21: 1506-068 (W) Operation between types "struct _z
val_struct**" and "int" is not allowed.
"zend_operators.c", line 581.34: 1506-275 (S) Unexpected text zval encountered.
"zend_operators.c", line 581.41: 1506-046 (S) Syntax error.
"zend_operators.c", line 581.21: 1506-068 (W) Operation between types "struct _z
val_struct**" and "int" is not allowed.
"zend_operators.c", line 596.34: 1506-275 (S) Unexpected text zval encountered.
"zend_operators.c", line 596.41: 1506-046 (S) Syntax error.
"zend_operators.c", line 596.21: 1506-068 (W) Operation between types "struct _z
val_struct**" and "int" is not allowed.
gmake[1]: *** [zend_operators.lo] Error 1
gmake[1]: Leaving directory `/Samba/holmberg/Apache/php-4.2.1/Zend'
gmake: *** [install-recursive] Error 1
#
-------------------------------------------------------

Please try this snapshot:

http://snaps.php.net/php4-latest.tar.gz

It compiled fine on AIX 4.3.3 yesterday. 
(I was using gcc though..)

I tried 'latest.tar.gz' and now get...

# ./configure --with-apache=../apache_1.3.26
loading cache ./config.cache
checking for Cygwin environment... (cached) no
checking for mingw32 environment... (cached) no
checking host system type... powerpc-ibm-aix4.3.1.0
checking how to run the C preprocessor... (cached) /lib/cpp
checking for AIX... no
checking for gcc... (cached) cc
checking whether the C compiler (cc -O -I/usr/local/ssl/include ) works... yes
checking whether the C compiler (cc -O -I/usr/local/ssl/include ) is a cross-com
piler... no
checking whether we are using GNU C... (cached) no
checking whether cc accepts -g... (cached) yes
......

# gmake
cc  -Iext/mysql/ -I/Samba/holmberg/Apache/php4-200207010900/ext/mysql/ -DPHP_ATO
M_INC -I/Samba/holmberg/Apache/php4-200207010900/include -I/Samba/holmberg/Apach
e/php4-200207010900/main -I/Samba/holmberg/Apache/php4-200207010900 -I/Samba/hol
mberg/Apache/php4-200207010900/Zend -I/Samba/holmberg/Apache/php4-200207010900/e
xt/xml/expat  -I/Samba/holmberg/Apache/php4-200207010900/TSRM -O -I/usr/local/ss
l/include  -c /Samba/holmberg/Apache/php4-200207010900/ext/mysql/php_mysql.c -o
ext/mysql/php_mysql.o  && echo > ext/mysql/php_mysql.lo
"/usr/include/sys/param.h", line 103.9: 1506-236 (W) Macro name MAXPATHLEN has b
een redefined.
"/usr/include/sys/param.h", line 103.9: 1506-358 (I) "MAXPATHLEN" is defined on
line 223 of /Samba/holmberg/Apache/php4-200207010900/main/php.h.
"/Samba/holmberg/Apache/php4-200207010900/TSRM/tsrm_config_common.h", line 27.2:
 1506-224 (I) Incorrect #pragma ignored.
"/Samba/holmberg/Apache/php4-200207010900/ext/mysql/php_mysql.c", line 65.11: 15
06-296 (S) #include file <mysql.h> not found.
"/Samba/holmberg/Apache/php4-200207010900/ext/mysql/php_mysql.c", line 113.9: 15
06-046 (S) Syntax error.
"/Samba/holmberg/Apache/php4-200207010900/ext/mysql/php_mysql.c", line 232.9: 15
06-045 (S) Undeclared identifier MYSQL_RES.
"/Samba/holmberg/Apache/php4-200207010900/ext/mysql/php_mysql.c", line 232.20: 1
506-045 (S) Undeclared identifier mysql_result.

And about 100 more syntax errors like the above.

The MySQL things can be solved by:
Installing autoconf 2.53 (maybe 2.52 works too)
rm configure
./buildconf
./configure --bla-bla

(the snapshots are generated with autoconf 2.13 which has some problems).

Derick

At least it doesn't fail with Zend now? :)
What was the configure line you used? 
Could you try and add '--without-mysql' so we know for sure
it's only mysql that doesn't compile..
(update the topic if it's so)

updated version. (you can ignore Derick's comment..the snapshots have configure generated with autoconf 2.53)

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.