Make morestack_unwind test work regardless of whether syscalls are patched for the first call or only for the second call

Author: rocallahan

src/test/x86/morestack_unwind.c

@@ -2,6 +2,11 @@
 
 #include "util.h"
 
+static void start_test(void) {
+  int break_here = 1;
+  (void)break_here;
+}
+
 static void breakpoint(void) {
   int break_here = 1;
   (void)break_here;
@@ -10,6 +15,8 @@ static void breakpoint(void) {
 int main(void) {
   // glibc write() might only be patched after the first time it is executed.
   atomic_puts("Ensure glibc write() is patched...");
+
+  start_test();
   // The test requires this write() be buffered:
   atomic_puts("EXIT-SUCCESS");
   breakpoint();

src/test/x86/morestack_unwind.py

@@ -1,6 +1,6 @@
 from util import *
 
-send_gdb('break main')
+send_gdb('break start_test')
 expect_gdb('Breakpoint 1')
 send_gdb('c')
 expect_gdb('Breakpoint 1')