Fix breakage caused by undefined behaviour. Using PTHREAD_CANCEL_ASYNCHRONOUS
is only allowed in pure functions.
See also: https://bugs.gentoo.org/show_bug.cgi?id=537516

--- linuxsampler-2.0.0/m4/nptl_bug.m4
+++ linuxsampler-2.0.0/m4/nptl_bug.m4
@@ -47,7 +47,7 @@
 void* __pthread_launcher(void* p) {
     // let the thread be killable under any circumstances
     // (without this function call, this test always succeeds !)
-    pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
+    pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, NULL);
 
     // this will block this 2nd thread, since we already
     // locked this mutex by the main thread