configure: Do not use pthread_create to check for pthread

Certain instrumentation addons leads to a false positive in configure
and link failures at the end of the build phase.
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

configure

@@ -3800,17 +3800,17 @@ fi
 # do this before the optional library checks as some of them require pthreads
 if ! disabled pthreads && ! enabled w32threads; then
     enable pthreads
-    if check_func pthread_create; then
+    if check_func pthread_join; then
         :
-    elif check_func pthread_create -pthread; then
+    elif check_func pthread_join -pthread; then
         add_cflags -pthread
         add_extralibs -pthread
-    elif check_func pthread_create -pthreads; then
+    elif check_func pthread_join -pthreads; then
         add_cflags -pthreads
         add_extralibs -pthreads
-    elif check_func pthread_create -lpthreadGC2; then
+    elif check_func pthread_join -lpthreadGC2; then
         add_extralibs -lpthreadGC2
-    elif ! check_lib pthread.h pthread_create -lpthread; then
+    elif ! check_lib pthread.h pthread_join -lpthread; then
         disable pthreads
     fi
 fi