[ruby/fiddle] Use have_header and have_type to detect memory view availability

Fix https://github.com/ruby/fiddle/pull/84

It may detect ruby/memory_view.h for system Ruby that is installed in
/usr.

We can use RUBY_API_VERSION_MAJOR to detect memory view availability
because memory view is available since Ruby 3.0.

Reported by Jun Aruga. Thanks!!!

https://github.com/ruby/fiddle/commit/3292929830

ext/fiddle/extconf.rb

@@ -222,10 +222,6 @@ types.each do |type, signed|
   end
 end
 
-if have_header("ruby/memory_view.h")
-  have_type("rb_memory_view_t", ["ruby/memory_view.h"])
-end
-
 if libffi
   $LOCAL_LIBS.prepend("./#{libffi.a} ").strip! # to exts.mk
   $INCFLAGS.gsub!(/-I#{libffi.dir}/, '-I$(LIBFFI_DIR)')

ext/fiddle/fiddle.h

@@ -2,6 +2,7 @@
 #define FIDDLE_H
 
 #include <ruby.h>
+#include <ruby/version.h>
 #include <errno.h>
 
 #if defined(_WIN32)
@@ -189,7 +190,7 @@
 #define ALIGN_INT32_T ALIGN_OF(int32_t)
 #define ALIGN_INT64_T ALIGN_OF(int64_t)
 
-#ifdef HAVE_TYPE_RB_MEMORY_VIEW_T
+#if RUBY_API_VERSION_MAJOR >= 3
 # define FIDDLE_MEMORY_VIEW
 #endif
 

ext/fiddle/memory_view.c

@@ -1,10 +1,11 @@
+#include <fiddle.h>
+
+#ifdef FIDDLE_MEMORY_VIEW
+
 #include <stdbool.h>
 #include <ruby/ruby.h>
 #include <ruby/encoding.h>
-
-#ifdef HAVE_RUBY_MEMORY_VIEW_H
-# include <ruby/memory_view.h>
-#endif
+#include <ruby/memory_view.h>
 
 #if SIZEOF_INTPTR_T == SIZEOF_LONG_LONG
 #   define INTPTR2NUM LL2NUM
@@ -17,9 +18,6 @@
 #   define UINTPTR2NUM UINT2NUM
 #endif
 
-#include <fiddle.h>
-
-#ifdef FIDDLE_MEMORY_VIEW
 VALUE rb_cMemoryView = Qnil;
 
 struct memview_data {

ext/fiddle/pointer.c

@@ -6,13 +6,13 @@
 #include <ruby/ruby.h>
 #include <ruby/io.h>
 
-#ifdef HAVE_RUBY_MEMORY_VIEW_H
-# include <ruby/memory_view.h>
-#endif
-
 #include <ctype.h>
 #include <fiddle.h>
 
+#ifdef FIDDLE_MEMORY_VIEW
+# include <ruby/memory_view.h>
+#endif
+
 #ifdef PRIsVALUE
 # define RB_OBJ_CLASSNAME(obj) rb_obj_class(obj)
 # define RB_OBJ_STRING(obj) (obj)