This patch adds end-to-end/breathing tests for coroutines
into libc++. The tests aren't specifically to test libc++ requirements
but instead are intented to ensure coroutines are working fine in general.
Although libc++ isn't exactly the most correct place for these tests
to live, there is one major advantage. The libc++ test suite is also
used by MSVC and by adding the tests here it ensures they will be
run against all currently available coroutine implementations.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@304101 91177308-0d34-0410-b5e6-96231b3b80d8
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