string.c: reduce duplicated code

* string.c (rb_str_cat, rb_str_cat2): reduce duplicated code, they
  are same as rb_str_buf_cat and rb_str_buf_cat2 respectively now.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45606 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
string.c: alias of rb_str_buf_cat and rb_str_buf_cat2

* string.c (rb_str_cat, rb_str_cat2): make aliases of
  rb_str_buf_cat and rb_str_buf_cat2 respectively.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45607 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
configure.in: FUNC_MINIMIZED

* configure.in (RUBY_FUNC_ATTRIBUTE): escape double quotes in
  attribute.

* configure.in (FUNC_MINIMIZED): attribute to minimize function
  body.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45608 b2dd03c8-39d4-4d8f-98ff-823fe69b080e