apart from the other errors, the constants aren't set anywhere in the source of php_curl nor libcurl.

Deleting intermediate files and output files for project 'curl - Win32 Release_TS'.
--------------------Configuration: curl - Win32 Release_TS--------------------
Compiling...
curl.c
D:\compile\php\php4-200105030645\ext\curl\curl.c(357) : error C2065: 'executor_globals' : undeclared identifier
D:\compile\php\php4-200105030645\ext\curl\curl.c(357) : error C2223: left of '->function_table' must point to struct/union
D:\compile\php\php4-200105030645\ext\curl\curl.c(359) : warning C4047: 'function' : 'struct _zval_struct ** ' differs in levels of indirection from 'struct _zval_struct *'
D:\compile\php\php4-200105030645\ext\curl\curl.c(359) : warning C4024: 'call_user_function' : different types for formal and actual parameter 2
D:\compile\php\php4-200105030645\ext\curl\curl.c(360) : warning C4047: 'function' : 'struct _zval_struct *' differs in levels of indirection from 'const int '
D:\compile\php\php4-200105030645\ext\curl\curl.c(360) : warning C4024: 'call_user_function' : different types for formal and actual parameter 4
D:\compile\php\php4-200105030645\ext\curl\curl.c(360) : warning C4047: 'function' : 'int ' differs in levels of indirection from 'struct _zval_struct *[3]'
D:\compile\php\php4-200105030645\ext\curl\curl.c(360) : warning C4024: 'call_user_function' : different types for formal and actual parameter 5
D:\compile\php\php4-200105030645\ext\curl\curl.c(360) : error C2198: 'call_user_function' : too few actual parameters
D:\compile\php\php4-200105030645\ext\curl\curl.c(398) : error C2223: left of '->function_table' must point to struct/union
D:\compile\php\php4-200105030645\ext\curl\curl.c(400) : warning C4047: 'function' : 'struct _zval_struct ** ' differs in levels of indirection from 'struct _zval_struct *'
D:\compile\php\php4-200105030645\ext\curl\curl.c(400) : warning C4024: 'call_user_function' : different types for formal and actual parameter 2
D:\compile\php\php4-200105030645\ext\curl\curl.c(401) : warning C4047: 'function' : 'struct _zval_struct *' differs in levels of indirection from 'const int '
D:\compile\php\php4-200105030645\ext\curl\curl.c(401) : warning C4024: 'call_user_function' : different types for formal and actual parameter 4
D:\compile\php\php4-200105030645\ext\curl\curl.c(401) : warning C4047: 'function' : 'int ' differs in levels of indirection from 'struct _zval_struct *[2]'
D:\compile\php\php4-200105030645\ext\curl\curl.c(401) : warning C4024: 'call_user_function' : different types for formal and actual parameter 5
D:\compile\php\php4-200105030645\ext\curl\curl.c(401) : error C2198: 'call_user_function' : too few actual parameters
D:\compile\php\php4-200105030645\ext\curl\curl.c(433) : error C2223: left of '->function_table' must point to struct/union
D:\compile\php\php4-200105030645\ext\curl\curl.c(435) : warning C4047: 'function' : 'struct _zval_struct ** ' differs in levels of indirection from 'struct _zval_struct *'
D:\compile\php\php4-200105030645\ext\curl\curl.c(435) : warning C4024: 'call_user_function' : different types for formal and actual parameter 2
D:\compile\php\php4-200105030645\ext\curl\curl.c(436) : warning C4047: 'function' : 'struct _zval_struct *' differs in levels of indirection from 'const int '
D:\compile\php\php4-200105030645\ext\curl\curl.c(436) : warning C4024: 'call_user_function' : different types for formal and actual parameter 4
D:\compile\php\php4-200105030645\ext\curl\curl.c(436) : warning C4047: 'function' : 'int ' differs in levels of indirection from 'struct _zval_struct *[3]'
D:\compile\php\php4-200105030645\ext\curl\curl.c(436) : warning C4024: 'call_user_function' : different types for formal and actual parameter 5
D:\compile\php\php4-200105030645\ext\curl\curl.c(436) : error C2198: 'call_user_function' : too few actual parameters
D:\compile\php\php4-200105030645\ext\curl\curl.c(523) : error C2065: 'CURLOPT_WRITEFUNCTIONDATA' : undeclared identifier
D:\compile\php\php4-200105030645\ext\curl\curl.c(525) : error C2065: 'CURLOPT_READFUNCTIONDATA' : undeclared identifier
D:\compile\php\php4-200105030645\ext\curl\curl.c(661) : error C2065: 'CURLOPT_HEADERFUNCTIONDATA' : undeclared identifier
Error executing xicl6.exe.

php_curl.dll - 10 error(s), 18 warning(s)