Emit warning when throw exception in destruct or dealloc functions which has a

Emit warning when throw exception in destruct or dealloc functions which has a
(possible implicit) noexcept specifier

Throwing in the destructor is not good (C++11 change try to not allow see below).
 But in reality, those codes are exist.
C++11 [class.dtor]p3:

A declaration of a destructor that does not have an exception-specification is
implicitly considered to have the same exception specification as an implicit
declaration.

With this change, the application worked before may now run into runtime
termination. My goal here is to emit a warning to provide only possible info to
where the code may need to be changed.

First there is no way, in compile time to identify the “throw” really throw out
of the function. Things like the call which throw out… To keep this simple,
when “throw” is seen, checking its enclosing function(only destructor and
dealloc functions) with noexcept(true) specifier emit warning.

Here is implementation detail:
A new member function CheckCXXThrowInNonThrowingFunc is added for class Sema
in Sema.h. It is used in the call to both BuildCXXThrow and
TransformCXXThrowExpr.

The function basic check if the enclosing function with non-throwing noexcept
specifer, if so emit warning for it.

The example of warning message like:
k1.cpp:18:3: warning: ''~dependent_warn'' has a (possible implicit) non-throwing

    noexcept specifier. Throwing exception may cause termination.
        [-Wthrow-in-dtor]
        throw 1;
        ^

        k1.cpp:43:30: note: in instantiation of member function

        'dependent_warn<noexcept_fun>::~dependent_warn' requested here

        dependent_warn<noexcept_fun> f; // cause warning

Differential Revision: https://reviews.llvm.org/D33333

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@306149 91177308-0d34-0410-b5e6-96231b3b80d8