constexpr: Implement the [dcl.constexpr]p5 check for whether a constexpr
function definition can produce a constant expression. This also provides the
last few checks for [dcl.constexpr]p3 and [dcl.constexpr]p4.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@149108 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed