If I try to compile php with --enable-wddx and --disable-sessions I get:

./.libs/libphp4.a(wddx.o): In function `ps_srlzr_encode_wddx':
wddx.o(.text+0x2ed): undefined reference to `ps_globals'
wddx.o(.text+0x312): undefined reference to `ps_globals'
wddx.o(.text+0x340): undefined reference to `php_get_session_var'
wddx.o(.text+0x36b): undefined reference to `ps_globals'
./.libs/libphp4.a(wddx.o): In function `ps_srlzr_decode_wddx':
wddx.o(.text+0x53a): undefined reference to `php_set_session_var'
wddx.o(.text+0x559): undefined reference to `ps_globals'
./.libs/libphp4.a(wddx.o): In function `zm_startup_wddx':
wddx.o(.text+0x5f6): undefined reference to `php_session_register_serializer'
collect2: ld returned 1 exit status
make[1]: *** [php] Error 1

If wddx depends on sessions, it should be checked at configure time no?