This change works around a couple of bugs:
1. EDG doesn't like explicit constexpr in a derived class. This program:
struct Base {};
struct Derived : Base {
constexpr Derived() = default;
};
triggers "error: defaulted default constructor cannot be constexpr."
2. C1XX with /Za has no idea which constructor needs to be valid for copy elision.
The change also conditionally disables parts of the msvc_stdlib_force_include.hpp header that conflict with external configuration when _LIBCXX_IN_DEVCRT is defined.
Differential Revision: https://reviews.llvm.org/D32778
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@302707 91177308-0d34-0410-b5e6-96231b3b80d8
f0346a5663