Michael van der Westhuizen: The attached patch add support for building against libc++abi and libcxxrt to CMake builds of libc++.

Usage (with the appropriate CC and CXX environment variables) is:
$ cmake -DLIBCXX_CXX_ABI=libcxxabi '-DLIBCXX_LIBCXXABI_INCLUDE_PATHS=/home/michael/libcxxabi/include' ../libcxx
and:
$ cmake -DLIBCXX_CXX_ABI=libcxxrt '-DLIBCXX_LIBCXXRT_INCLUDE_PATHS=/home/michael/libcxxrt/src' ../libcxx

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@174623 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/vector b/include/vector
index 876b7e5..f4a41d6 100644
--- a/include/vector
+++ b/include/vector
@@ -440,7 +440,7 @@
 __vector_base<_Tp, _Allocator>::__destruct_at_end(const_pointer __new_last, false_type) _NOEXCEPT
 {
     while (__new_last != __end_)
-        __alloc_traits::destroy(__alloc(), const_cast<pointer>(--__end_));
+        __alloc_traits::destroy(__alloc(), _VSTD::__to_raw_pointer(--__end_));
 }
 
 template <class _Tp, class _Allocator>
@@ -448,7 +448,7 @@
 void
 __vector_base<_Tp, _Allocator>::__destruct_at_end(const_pointer __new_last, true_type) _NOEXCEPT
 {
-    __end_ = const_cast<pointer>(__new_last);
+    __end_ = static_cast<pointer>(__new_last);
 }
 
 template <class _Tp, class _Allocator>
@@ -1550,7 +1550,7 @@
         "vector::erase(iterator) called with an iterator not"
         " referring to this vector");
 #endif
-    pointer __p = const_cast<pointer>(&*__position);
+    pointer __p = this->__begin_ + (__position - cbegin());
     iterator __r = __make_iter(__p);
     this->__destruct_at_end(_VSTD::move(__p + 1, this->__end_, __p));
     return __r;