configure.in: fix for old Apple compilers

* configure.in (__builtin_setjmp): disable with gcc/clang earlier
  than 4.3 on Mac OS X.  [ruby-core:65174] [Bug #10272]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48184 b2dd03c8-39d4-4d8f-98ff-823fe69b080e