mesa: Define introspection macro to determine whether a type is trivially destructible.

Only implemented on GCC and Clang for now.  Other compilers use a
dummy implementation that always returns false, which should be a safe
[but slightly inefficient] assumption in all cases.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/mesa/main/compiler.h

@@ -444,7 +444,29 @@ do {                                                                    \
 #define Elements(x) (sizeof(x)/sizeof(*(x)))
 #endif
 
-
+#ifdef __cplusplus
+/**
+ * Macro function that evaluates to true if T is a trivially
+ * destructible type -- that is, if its (non-virtual) destructor
+ * performs no action and all member variables and base classes are
+ * trivially destructible themselves.
+ */
+#   if defined(__GNUC__)
+#      if ((__GNUC__ > 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 3)))
+#         define HAS_TRIVIAL_DESTRUCTOR(T) __has_trivial_destructor(T)
+#      endif
+#   elif (defined(__clang__) && defined(__has_feature))
+#      if __has_feature(has_trivial_destructor)
+#         define HAS_TRIVIAL_DESTRUCTOR(T) __has_trivial_destructor(T)
+#      endif
+#   endif
+#   ifndef HAS_TRIVIAL_DESTRUCTOR
+       /* It's always safe (if inefficient) to assume that a
+        * destructor is non-trivial.
+        */
+#      define HAS_TRIVIAL_DESTRUCTOR(T) (false)
+#   endif
+#endif
 
 #ifdef __cplusplus
 }