Allow a using directive to refer to the implicitly-defined namespace
"std", with a warning, to improve GCC compatibility. Fixes PR7517.

As a drive-by, add typo correction for using directives.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@107172 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed