Add support for function attribute 'not_tail_called'.

Add support for function attribute 'not_tail_called'.

This attribute is used to prevent tail-call optimizations to the marked
function. For example, in the following piece of code, foo1 will not be
tail-call optimized:

int __attribute__((not_tail_called)) foo1(int);

int foo2(int a) {
  return foo1(a); // Tail-call optimization is not performed.
}

The attribute has effect only on statically bound calls. It has no
effect on indirect calls. Also, virtual functions and objective-c
methods cannot be marked as 'not_tail_called'.

rdar://problem/22667622

Differential Revision: http://reviews.llvm.org/D12922

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@252369 91177308-0d34-0410-b5e6-96231b3b80d8