move alloca() definition from all *.h files to one new header file

plugin/cracklib_password_check/cracklib_password_check.c

@@ -13,7 +13,7 @@
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */
 
-#include <my_global.h>
+#include <my_alloca.h>
 #include <mysql/plugin_password_validation.h>
 #include <crack.h>
 #include <string.h>

plugin/handler_socket/handlersocket/hstcpsvr_worker.cpp

@@ -6,7 +6,7 @@
  * See COPYRIGHT.txt for details.
  */
 
-#include <my_global.h>
+#include <my_alloca.h>
 #include <netinet/in.h>
 #include <errno.h>
 #include <poll.h>
@@ -17,9 +17,6 @@
 #if __linux__
 #include <sys/epoll.h>
 #endif
-#ifdef HAVE_ALLOCA_H
-#include <alloca.h>
-#endif
 
 #include "hstcpsvr_worker.hpp"
 #include "string_buffer.hpp"

plugin/handler_socket/libhsclient/allocator.hpp

@@ -11,6 +11,7 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <my_alloca.h>
 
 #if 0
 extern "C" {