[Feature #18249] Include ruby.h in extensions to have ABI version

All shared libraries must have `include/ruby/internal/abi.h` to include
the ABI version. Including `ruby.h` will guarantee that.

enc/encinit.c.erb

@@ -2,6 +2,7 @@
  * Author: yugui@google.com (Yugui Sonoda)
  */
 #include <stdio.h>
+#include "ruby.h"
 
 #define init(func, name) {	\
     extern void func(void);	\

enc/trans/transdb.c

@@ -9,6 +9,8 @@
 
 **********************************************************************/
 
+#include "ruby.h"
+
 void rb_declare_transcoder(const char *enc1, const char *enc2, const char *lib);
 
 void

ext/-test-/load/dot.dot/dot.dot.c

@@ -1 +1,3 @@
+#include "ruby.h"
+
 void Init_dot(void) {}

regenc.h

@@ -51,6 +51,8 @@
 # undef ONIG_ESCAPE_UCHAR_COLLISION
 #endif
 
+#include "ruby.h"
+
 #ifdef RUBY
 # include "ruby/onigmo.h"
 #else