Bug#8391 - "merge" fails on Linux/IA64

It was a thread stack overrun.
IA64 had its own stack size section already.
Enlarged its default stack size from 192K to 256K.

include/my_pthread.h

@@ -637,7 +637,7 @@ extern int pthread_dummy(int);
   MySQL can survive with 32K, but some glibc libraries require > 128K stack
   To resolve hostnames
 */
-#define DEFAULT_THREAD_STACK	(192*1024L)
+#define DEFAULT_THREAD_STACK	(256*1024L)
 #else
 #define DEFAULT_THREAD_STACK	(192*1024)
 #endif