PR20546: Fix tests for compare_exchange_weak.

These calls are allowed to fail spuriously.

29.6.5.25:

    Remark: A weak compare-and-exchange operation may fail spuriously.
    That is, even when the contents of memory referred to by expected
    and object are equal, it may return false and store back to expected
    the same memory contents that were originally there. [ Note: This
    spurious failure enables implementation of compare and-exchange on a
    broader class of machines, e.g., load-locked store-conditional
    machines. A consequence of spurious failure is that nearly all uses
    of weak compare-and-exchange will be in a loop.

To fix this, we replace any assert() that expects
std::atomic::compare_exchange_weak() to return true with a loop. If the
call does not return true within N runs (with N currently equal to 10),
then the test fails.

http://llvm.org/bugs/show_bug.cgi?id=20546


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@217319 91177308-0d34-0410-b5e6-96231b3b80d8
Some of the synopsis was left out of these headers, and the copy construction/assignment should have been marked as deleted. Done. No functionality change, because the base class (base_ios) was marked as non-copyable already.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@217876 91177308-0d34-0410-b5e6-96231b3b80d8
Forgot 'const' on my last checkin

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@217877 91177308-0d34-0410-b5e6-96231b3b80d8
Fix a bad noexcept clause in tuple's move constructor

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@217878 91177308-0d34-0410-b5e6-96231b3b80d8
Thanks to K-ballo for noting a second incorrect noexcept clause in tuple - and suggesting a more correct way to write the first


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@217884 91177308-0d34-0410-b5e6-96231b3b80d8
Merge branch 'upstream'
[12] valarray for MSVC

- MSVC has trouble parsing a dependent type via an injected name, so fully spell it out
- Add a missing using ::abs
- Have basic_string be more friendly, otherwise MSVC attempts to instantiate valarray's operators