Disable init-order checking before destructors are run.

We don't want to report initialization-order bugs when a destructor of a global
variable accesses dynamically initialized global from another
(not necessarily initialized) module. We do this by intercepting __cxa_atexit and
registrering our own callback that unpoisons shadow for all dynamically initialized
global variables.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@182637 91177308-0d34-0410-b5e6-96231b3b80d8