[SemaCXX] Unconfuse Clang when std::align_val_t is unscoped in C++03

[SemaCXX] Unconfuse Clang when std::align_val_t is unscoped in C++03

When -faligned-allocation is specified in C++03 libc++ defines
std::align_val_t as an unscoped enumeration type (because Clang didn't
provide scoped enumerations as an extension until 8.0).
Unfortunately Clang confuses the `align_val_t` overloads of delete with
the sized deallocation overloads which aren't enabled. This caused Clang
to call the aligned deallocation function as if it were the sized
deallocation overload.

For example: https://godbolt.org/z/xXJELh

This patch fixes the confusion.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@351294 91177308-0d34-0410-b5e6-96231b3b80d8