llvm doesn't care about your size

They apparently removed alloc_size at some point (it was a no-op
beforehand), causing the attribute to throw an error when clang compiles
anything including allocator.h.

src/allocator.h

@@ -33,11 +33,22 @@ typedef struct HAllocator_ {
 typedef struct HArena_ HArena ; // hidden implementation
 
 HArena *h_new_arena(HAllocator* allocator, size_t block_size); // pass 0 for default...
-#ifndef SWIG
+
-void* h_arena_malloc(HArena *arena, size_t count) __attribute__(( malloc, alloc_size(2) ));
+#if defined __llvm__
+# if __has_attribute(malloc)
+#   define ATTR_MALLOC(n) __attribute__((malloc))
+# else
+#   define ATTR_MALLOC(n)
+# endif
+#elif defined SWIG
+# define ATTR_MALLOC(n)
+#elif defined __GNUC__
+# define ATTR_MALLOC(n) __attribute__((malloc, alloc_size(2)))
 #else
-void* h_arena_malloc(HArena *arena, size_t count);
+# define ATTR_MALLOC(n)
 #endif
+
+void* h_arena_malloc(HArena *arena, size_t count) ATTR_MALLOC(2);
 void h_arena_free(HArena *arena, void* ptr); // For future expansion, with alternate memory managers.
 void h_delete_arena(HArena *arena);