Disable aligned new/delete on Apple platforms without posix_memalign

Summary:
This patch disables the aligned new/delet overloads on Apple platforms without `posix_memalign`. This fixes libc++.dylib build regressions on such platforms.
This fixes http://llvm.org/PR31448.

This patch should also be merged into the 4.0 release branch


Reviewers: mclow.lists, rsmith, dexonsmith, jeremyhu

Reviewed By: mclow.lists

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D28931

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@292564 91177308-0d34-0410-b5e6-96231b3b80d8

src/new.cpp

@@ -151,6 +151,8 @@ operator delete[] (void* ptr, size_t) _NOEXCEPT
     ::operator delete[](ptr);
 }
 
+#if !defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION)
+
 _LIBCPP_WEAK
 void *
 operator new(std::size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC
@@ -275,6 +277,8 @@ operator delete[] (void* ptr, size_t, std::align_val_t alignment) _NOEXCEPT
     ::operator delete[](ptr, alignment);
 }
 
+#endif // !defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION)
+
 #endif // !__GLIBCXX__
 
 namespace std