Please try using this CVS snapshot:

  http://snaps.php.net/php5-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php5-win32-latest.zip

And check config.log for possible more information about the error.

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configure with pcntl works

configure 5.0.0RC1 failed here too on Linux Kernel 2.4, but I found the solution in the config.log file. The test compilation for the fork() function called by configure links against -liodbc.
Workaround: install the libodbc header files and configure acts as expected.

configure: error: pcntl: fork() not supported by this platform

same problem on HP-UX 11.00 with lastest release ( php5-200408030630 ) and with official release of php 5 ...

First time i try to include this module with php...

my config.log:

configure:66083: checking for fork
configure:66111: gcc -o conftest -g -O2   -L/opt/oracle/product/9i_client/lib -L/opt/oracle/product/9i_client/lib conftest.c -lm -lnsl  -l:libcl.sl -l:librt.sl -l:libnss_dns.1 -l:libdld.sl -lclntsh 1>&5
/var/tmp//ccBi6ulb.s: Assembler messages:
/var/tmp//ccBi6ulb.s:41: Warning: .stabs: description field '10231' too big, try a different debug format
/var/tmp//ccBi6ulb.s:45: Warning: .stabn: description field '10231' too big, try a different debug format
/var/tmp//ccBi6ulb.s:51: Warning: .stabn: description field '10239' too big, try a different debug format
/var/tmp//ccBi6ulb.s:56: Warning: .stabn: description field '1023c' too big, try a different debug format
/usr/ccs/bin/ld: /opt/oracle/product/9i_client/lib/libclntsh.sl: Mismatched ABI. 64-bit PA shared library found in 32-bit link.
collect2: ld returned 1 exit status
configure: failed program was:
#line 66088 "configure"
#include "confdefs.h"
/* System header to define __stub macros and hopefully few prototypes,
    which can conflict with char fork(); below.  */
#include <assert.h>
/* Override any gcc2 internal prototype to avoid an error.  */
/* We use char because int might match the return type of a gcc2
    builtin and then its argument prototype would still apply.  */
char fork();

int main() {

/* The GNU C library defines this for functions which it implements
    to always fail with ENOSYS.  Some functions are actually named
    something starting with __ and the normal name is an alias.  */
#if defined (__stub_fork) || defined (__stub___fork)
choke me
#else
fork();
#endif

; return 0; }

my config.log:

configure:66083: checking for fork
configure:66111: gcc -o conftest -g -O2   -L/opt/oracle/product/9i_client/lib -L/opt/oracle/product/9i_client/lib conftest.c -lm -lnsl  -l:libcl.sl -l:librt.sl -l:libnss_dns.1 -l:libdld.sl -lclntsh 1>&5
/var/tmp//ccBi6ulb.s: Assembler messages:
/var/tmp//ccBi6ulb.s:41: Warning: .stabs: description field '10231' too big, try a different debug format
/var/tmp//ccBi6ulb.s:45: Warning: .stabn: description field '10231' too big, try a different debug format
/var/tmp//ccBi6ulb.s:51: Warning: .stabn: description field '10239' too big, try a different debug format
/var/tmp//ccBi6ulb.s:56: Warning: .stabn: description field '1023c' too big, try a different debug format
/usr/ccs/bin/ld: /opt/oracle/product/9i_client/lib/libclntsh.sl: Mismatched ABI. 64-bit PA shared library found in 32-bit link.
collect2: ld returned 1 exit status
configure: failed program was:
#line 66088 "configure"
#include "confdefs.h"
/* System header to define __stub macros and hopefully few prototypes,
    which can conflict with char fork(); below.  */
#include <assert.h>
/* Override any gcc2 internal prototype to avoid an error.  */
/* We use char because int might match the return type of a gcc2
    builtin and then its argument prototype would still apply.  */
char fork();

int main() {

/* The GNU C library defines this for functions which it implements
    to always fail with ENOSYS.  Some functions are actually named
    something starting with __ and the normal name is an alias.  */
#if defined (__stub_fork) || defined (__stub___fork)
choke me
#else
fork();
#endif

; return 0; }