strengthen test_alloca to check alignment

tests/core/test_alloca.in

@@ -1,9 +1,14 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include <assert.h>
 
-int main() {
-  char *pc;
-  pc = (char *)alloca(5);
-  printf("z:%d*%d*\n", pc > 0, (int)pc);
+int main(int argc, char **argv) {
+  char *pc, *pc2;
+  assert(argc == 1);
+  pc = (char *)alloca(4+argc);
+  assert(((int)pc) % 4 == 0);
+  pc2 = (char *)alloca(4+argc);
+  assert(((int)pc2) % 4 == 0);
+  printf("z:%d*%d*%d*\n", pc > 0, (int)pc, (int)pc2);
   return 0;
 }

tests/test_core.py

@@ -1606,6 +1606,8 @@ class T(RunnerCore): # Short name, to make it more fun to use manually on the co
       self.do_run_from_file(src, output)
 
   def test_alloca(self):
+    if Settings.USE_TYPED_ARRAYS != 2: return self.skip('non-ta2 may have unaligned allocas')
+
     test_path = path_from_root('tests', 'core', 'test_alloca')
     src, output = (test_path + s for s in ('.in', '.out'))