[libc++] Fix incorrect definition of TEST_HAS_C11_FEATURES

Summary:
The macro was not defined in C++11 mode when it should have been, at least
according to how _LIBCPP_HAS_C11_FEATURES is defined.

Reviewers: mclow.lists, EricWF, jfb, dexonsmith

Subscribers: christof, dexonsmith, cfe-commits

Differential Revision: https://reviews.llvm.org/D50719

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@339702 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed