Move _LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS macro to build system

[tzik]

Summary

_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS is currently used to
bring back std::unexpected, which is removed in C++17, but still needed
for libc++abi for backward compatibility.

This macro used to define in cxa_exception.cpp only, but actually
needed for all sources that touches exceptions.
So, a build-system-level macro is better fit to define this macro.

[tzik]

rsmith: Could you PTAL to this? This is an attempt to resolve https://bugs.llvm.org/show_bug.cgi?id=34103.
Though we already have a way to bring back std::unexpected to libc++abi, we currently don't apply it properly, IMO.

[rsmith]

This looks right to me.

[tzik]

rsmith: Thanks! I don't have the commit access to the repository. Could you submit this for me?

[thakis]

Landed in r331150: http://llvm.org/viewvc/llvm-project?view=revision&revision=331150

[thakis]

Apologies for misspelling your last name :-(

CMakeLists.txt

 
 if (LIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY)
   add_definitions(-D_LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL)
 endif()
 
 # Prevent libc++abi from having library dependencies on libc++
 add_definitions(-D_LIBCPP_DISABLE_EXTERN_TEMPLATE)
 
+# Bring back `std::unexpected`, which is removed in C++17, to support
+# pre-C++17.
+add_definitions(-D_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS)
+
 if (MSVC)
   add_definitions(-D_CRT_SECURE_NO_WARNINGS)
 endif()
 
 # Define LIBCXXABI_USE_LLVM_UNWINDER for conditional compilation.
 if (LIBCXXABI_USE_LLVM_UNWINDER)
   add_definitions(-DLIBCXXABI_USE_LLVM_UNWINDER)
 endif()

src/cxa_exception.cpp

 //===------------------------- cxa_exception.cpp --------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //  
 //  This file implements the "Exception Handling APIs"
 //  http://mentorembedded.github.io/cxx-abi/abi-eh.html
 //  
 //===----------------------------------------------------------------------===//
 
-#define _LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS
-
 #include "cxxabi.h"
 
 #include <exception>        // for std::terminate
 #include <cstring>          // for memset
 #include "cxa_exception.hpp"
 #include "cxa_handlers.hpp"
 #include "fallback_malloc.h"
 #include "include/atomic_support.h"

test/test_exception_storage.pass.cpp

 //===-------------------- test_exception_storage.cpp ----------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
-// FIXME: cxa_exception.hpp directly references `std::unexpected` and friends.
-// This breaks this test when compiled in C++17. For now fix this by manually
-// re-enabling the STL functions.
-#define _LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS
-
 #include <cstdlib>
 #include <algorithm>
 #include <iostream>
 #include <__threading_support>
 #include <unistd.h>
 
 #include "../src/cxa_exception.hpp"