Fix tests for MSVC

warnings-as-errors caused the simple_seg_storage and threading tests to fail on all Visual C++ compilers. This define suppresses the warnings about unchecked iterators, which I don't think are solvable in a portable way.
Update test_poisoned_macros.cpp

Current test fails inside /boost/core/demangle.hpp: not sure why that header is even included, but anyway this fix solves the issue while preserving the intent of the test.
Merge pull request #4 from jzmaddock/patch-1

Update test_poisoned_macros.cpp
Merge pull request #3 from MarcelRaad/patch-1

Fix tests for MSVC

I don't have access to Windows machine but this patch looks okay.
Merge pull request #5 from boostorg/develop

Merge fixes into master

Tested fix on Darwin, works fine.