Fix build issues caused by Lazy Imports 3.14t

Summary:
The land of Lazy Imports in 3.14t (D85977460) led to Github test failures (e.g. T244893771).  [This](https://github.com/facebookincubator/cinder/actions/runs/19307995749) is the link to the builds/tests run on the change.
Although some of the issues were pre-existing, some of them were due to the Lazy Imports
3.14t change:
- Windows build errors ([example](https://github.com/facebookincubator/cinder/actions/runs/19307995749/job/55220483261)): These seem likely due to not defining `_Py_atomic_load_uchar_acquire()` and `_Py_atomic_store_uchar_release()` in `pyatomic_msc.h`
- macOS (free-threading) build error ([link](https://github.com/facebookincubator/cinder/actions/runs/19307995749/job/55220483210)): This is likely due to having a label immediately followed by a declaration in `dictobject.c`, which is not allowed sometimes in C (I think before C-23).

Reviewed By: itamaro

Differential Revision: D86888783

fbshipit-source-id: 0ccd7e86e17ac7a05ddc6f39b96022741d9b6312

Author: Subbarao Garlapati

Include/cpython/pyatomic_msc.h

@@ -1154,6 +1154,30 @@ _Py_atomic_load_ssize_acquire(const Py_ssize_t *obj)
 #endif
 }
 
+static inline void
+_Py_atomic_store_uchar_release(unsigned char *obj, unsigned char value)
+{
+#if defined(_M_X64) || defined(_M_IX86)
+    *(unsigned char volatile *)obj = value;
+#elif defined(_M_ARM64)
+    __stlr8((unsigned __int8 volatile *)obj, (unsigned __int8)value);
+#else
+#  error "no implementation of _Py_atomic_store_uchar_release"
+#endif
+}
+
+static inline unsigned char
+_Py_atomic_load_uchar_acquire(const unsigned char *obj)
+{
+#if defined(_M_X64) || defined(_M_IX86)
+    return *(unsigned char volatile *)obj;
+#elif defined(_M_ARM64)
+    return (unsigned char)__ldar8((unsigned __int8 volatile *)obj);
+#else
+#  error "no implementation of _Py_atomic_load_uchar_acquire"
+#endif
+}
+
 // --- _Py_atomic_fence ------------------------------------------------------
 
  static inline void

Objects/dictobject.c

@@ -1941,7 +1941,7 @@ Py_ssize_t
 _Py_dict_lookup_threadsafe_stackref(PyDictObject *mp, PyObject *key, Py_hash_t hash, _PyStackRef *value_addr)
 {
 #ifdef ENABLE_LAZY_IMPORTS
-start:
+start:;
 #endif
     PyDictKeysObject *dk = _Py_atomic_load_ptr(&mp->ma_keys);
     if (DK_KIND(dk) == DICT_KEYS_UNICODE && PyUnicode_CheckExact(key)) {