Fix the creation of stack integrity cookie (if used in the build) in pthread startup routine so that calling functions that check the validity of the stack is safe from pthreads.

Author: juj

src/pthread-main.js

@@ -77,6 +77,9 @@ this.onmessage = function(e) {
     assert(STACK_MAX > STACK_BASE);
     Runtime.establishStackSpace(e.data.stackBase, e.data.stackBase + e.data.stackSize);
     var result = 0;
+//#if STACK_OVERFLOW_CHECK
+    if (typeof writeStackCookie === 'function') writeStackCookie();
+//#endif
 
     PThread.receiveObjectTransfer(e.data);
 
@@ -90,6 +93,10 @@ this.onmessage = function(e) {
       } else {
         result = Module['asm'].dynCall_i(e.data.start_routine); // as a hack, try signature 'i' as fallback.
       }
+//#if STACK_OVERFLOW_CHECK
+      if (typeof checkStackCookie === 'function') checkStackCookie();
+//#endif
+
     } catch(e) {
       if (e === 'Canceled!') {
         PThread.threadCancel();