Revert "intrin.h: include setjmp.h to get a jmp_buf definition"

This failed the ms-intrin.cpp test.

This reverts commit r200237.

This also comments out the _setjmpex declaration for now so that
intrin.h will work on x64 targets.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@200243 91177308-0d34-0410-b5e6-96231b3b80d8