Introduce _LIBCPP_DEPRECATED_ABI_EXTERNAL_ERROR_CATEGORY_CONSTRUCTOR ABI option.

Currently libc++ compiles a special version of error_category()
into the dylib. This definition is no longer needed, and doesn't
work on Windows due to dllimport/dllexport semantics.

For those reasons this patch introduces an option to
disable/enable this definition. By default the definition
is provided in ABI v1 except on windows. This patch
also addresses D28210.

llvm-svn: 290840

libcxx/include/__config

@@ -53,6 +53,10 @@
 // of nullptr_t. This option is ABI incompatible with GCC in C++03 mode.
 #define _LIBCPP_ABI_ALWAYS_USE_CXX11_NULLPTR
 #elif _LIBCPP_ABI_VERSION == 1
+#if !defined(_WIN32)
+// Enable compiling a definition of error_category() into the libc++ dylib.
+#define _LIBCPP_DEPRECATED_ABI_EXTERNAL_ERROR_CATEGORY_CONSTRUCTOR
+#endif
 // Feature macros for disabling pre ABI v1 features. All of these options
 // are deprecated.
 #if defined(__FreeBSD__)

libcxx/include/system_error

@@ -384,7 +384,8 @@ class _LIBCPP_TYPE_VIS error_category
 public:
     virtual ~error_category() _NOEXCEPT;
 
-#ifdef _LIBCPP_BUILDING_SYSTEM_ERROR
+#if defined(_LIBCPP_BUILDING_SYSTEM_ERROR) && \
+    defined(_LIBCPP_DEPRECATED_ABI_EXTERNAL_ERROR_CATEGORY_CONSTRUCTOR)
     error_category() _NOEXCEPT;
 #else
     _LIBCPP_ALWAYS_INLINE

libcxx/src/system_error.cpp

@@ -29,9 +29,11 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 // class error_category
 
+#if defined(_LIBCPP_DEPRECATED_ABI_EXTERNAL_ERROR_CATEGORY_CONSTRUCTOR)
 error_category::error_category() _NOEXCEPT
 {
 }
+#endif
 
 error_category::~error_category() _NOEXCEPT
 {