configure.in: quote defun names

* configure.in (RUBY_TRY_CFLAGS, RUBY_TRY_LDFLAGS),
  (RUBY_CHECK_BUILTIN_SETJMP, RUBY_SETJMP_TYPE),
  (RUBY_STACK_GROW_DIRECTION): quote defun names, for some
  versions of autoconf possibly.  [ruby-core:64473] [Bug #10156]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47226 b2dd03c8-39d4-4d8f-98ff-823fe69b080e