configure.in: no -include options

* configure.in (XCFLAGS): stop including missing.h by command line
  option, as the header seems included necessary places already.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40123 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

configure.in

@@ -419,7 +419,7 @@ AC_SUBST(LD)
 if test "$GCC" = yes; then
     linker_flag=-Wl,
     : ${optflags=-O3}
-    RUBY_APPEND_OPTIONS(XCFLAGS, ["-include ruby/config.h" "-include ruby/missing.h"])
+    # RUBY_APPEND_OPTIONS(XCFLAGS, ["-include ruby/config.h" "-include ruby/missing.h"])
 else
     linker_flag=
 fi