CodeGen: force builtins to be local

Unfortunately _setjmp3 can be both import or local.  The ASAN tests try to
emulate the flags which makes this harder to detect.  Rely on the linker
creating or using thunks here instead.  Should repair the ASAN windows bots.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@289783 91177308-0d34-0410-b5e6-96231b3b80d8