Initial support for C++11 constexpr function invocation substitution. Using
constexpr function arguments outside of their function (passing or returning
them by reference) does not work correctly yet.

Calling constexpr function templates does not work yet, since the bodies are not
instantiated until the end of the translation unit.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@143234 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed