Configure freezing on pthreads_cflags?

I searched the archives and found a couple posts asking a similar question to this, but there never seemed to be a solution. Trying to build PHP 4.2.3 on a Redhat Linux 6.2 system, as a DSO along with Apache 1.3.27. Built perfectly fine yesterday on an (as far as I know) identical server using the same parameters. ./configure --with-pgsql --with-apxs=/usr/local/apache/bin/apxs Configure goes through its normal thing, but stops and just hangs forever at this line: checking for pthreads_cflags... After a while I killed it and looked at config.log. Here's what was at the end. Any help is appreciated. configure:2761: checking whether yytext is a pointer configure:2780: gcc -o conftest -g -O2 conftest.c -lfl 1>&5 configure:2804: checking for working const configure:2858: gcc -c -g -O2 conftest.c 1>&5 configure:3006: gcc -o conftest -g -O2 conftest.c 1>&5 /tmp/cczmrsba.o: In function `main': /usr/local/src/php-4.2.3/configure:3001: undefined reference to `pthread_mutexattr_init' /usr/local/src/php-4.2.3/configure:3002: undefined reference to `pthread_create' collect2: ld returned 1 exit status configure: failed program was: #line 2988 "configure" #include "confdefs.h" #include <pthread.h> #include <stddef.h> void *thread_routine(void *data) {

    return data;

} int main() {

    pthread_t thd;
    pthread_mutexattr_t mattr;
    int data = 1;
    pthread_mutexattr_init(&mattr);
    return pthread_create(&thd, NULL, thread_routine, &data);

} configure:3026: checking for pthreads_cflags configure:3059: gcc -o conftest -g -O2 -kthread conftest.c 1>&5 gcc: unrecognized option `-kthread' /tmp/ccWDMtpu.o: In function `main': /usr/local/src/php-4.2.3/configure:3054: undefined reference to `pthread_mutexattr_init' /usr/local/src/php-4.2.3/configure:3055: undefined reference to `pthread_create' collect2: ld returned 1 exit status configure: failed program was: #line 3041 "configure" #include "confdefs.h" #include <pthread.h> #include <stddef.h> void *thread_routine(void *data) {

    return data;

} int main() {

    pthread_t thd;
    pthread_mutexattr_t mattr;
    int data = 1;
    pthread_mutexattr_init(&mattr);
    return pthread_create(&thd, NULL, thread_routine, &data);

} configure:3059: gcc -o conftest -g -O2 -pthread conftest.c 1>&5