* configure.in (ac_cv_func___builtin_setjmp): gcc 4.9 disallows a
variable as the second argument of __builtin_longjmp().
[ruby-core:61800] [Bug #9692]
* configure.in (ac_cv_func___builtin_setjmp): __builtin_longjmp() in
clang 5.1 uses `void**`, not `jmp_buf`. [Bug #9692]
* configure.in (ac_cv_func___builtin_setjmp): __builtin_longjmp()
in Apple LLVM 5.1 (LLVM 3.4svn) uses `void**`, not `jmp_buf`.
[Bug #9692]
merge revision(s) r45503,r45504,r45508,r45509,r47275: [Backport #9692]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@47276 b2dd03c8-39d4-4d8f-98ff-823fe69b080e