[X86][CET] Shadow stack fix for setjmp/longjmp

This is the new version of D46181, allowing setjmp/longjmp
to work correctly with the Intel CET shadow stack by storing
SSP on setjmp and fixing it on longjmp. The patch has been
updated to use the cf-protection-return module flag instead
of HasSHSTK, and the bug that caused D46181 to be reverted
has been fixed with the test expanded to track that fix.

patch by mike.dvoretsky

Differential Revision: https://reviews.llvm.org/D47311

llvm-svn: 333990