refactored __attribute__ conditional insertion to cater for potential warnings

include/boost/poly_collection/detail/stride_iterator.hpp

@@ -73,6 +73,23 @@ public:
   explicit stride_iterator(DerivedValue* x)noexcept:
     p{x},stride_{sizeof(DerivedValue)}{}
 
+#if BOOST_WORKAROUND(BOOST_GCC_VERSION,>=40900)||\
+    BOOST_WORKAROUND(BOOST_CLANG,>=1)&&\
+    (__clang_major__>3 || __clang_major__==3 && __clang_minor__ >= 8)
+/* https://github.com/boostorg/poly_collection/issues/15 */
+  
+#define BOOST_POLY_COLLECTION_NO_SANITIZE
+
+/* UBSan seems not to be supported in some environments */
+#if defined(BOOST_GCC_VERSION)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wattributes"
+#elif defined(BOOST_CLANG)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wattributes"
+#endif
+#endif
+
   template<
     typename DerivedValue,
     typename std::enable_if<
@@ -80,16 +97,22 @@ public:
       (!std::is_const<Value>::value||std::is_const<DerivedValue>::value)
     >::type* =nullptr
   >
-#if BOOST_WORKAROUND(BOOST_GCC_VERSION,>=40900)||\
+#if defined(BOOST_POLY_COLLECTION_NO_SANITIZE)
-    BOOST_WORKAROUND(BOOST_CLANG,>=1)&&\
-    (__clang_major__>3 || __clang_major__==3 && __clang_minor__ >= 8)
-  /* https://github.com/boostorg/poly_collection/issues/15 */
-  
   __attribute__((no_sanitize("undefined")))
 #endif
   explicit operator DerivedValue*()const noexcept
   {return static_cast<DerivedValue*>(p);}
 
+#if defined(BOOST_POLY_COLLECTION_NO_SANITIZE)
+#if defined(BOOST_GCC_VERSION)
+#pragma GCC diagnostic pop
+#elif defined(BOOST_CLANG)
+#pragma clang diagnostic pop
+#endif
+
+#undef BOOST_POLY_COLLECTION_NO_SANITIZE
+#endif
+
   std::size_t stride()const noexcept{return stride_;}
 
 private: