Move main out of the extern "C" block in test_rust_gxx_personality_v0 (#22336)

llvm/llvm-project#101853 started to enforce the
C++ standard langauge that disallows main from being declared in a
linkage specification.

Author: dschuff

test/test_other.py

@@ -13990,10 +13990,10 @@ def test_rust_gxx_personality_v0(self):
       #include <stdint.h>
       extern "C" {
         int __gxx_personality_v0(int version, void* actions, uint64_t exception_class, void* exception_object, void* context);
-        int main() {
-          __gxx_personality_v0(0, NULL, 0, NULL, NULL);
-          return 0;
-        }
+      }
+      int main() {
+        __gxx_personality_v0(0, NULL, 0, NULL, NULL);
+        return 0;
       }
     ''', assert_returncode=NON_ZERO, emcc_args=['-fexceptions'])