[libc++abi] Default to DLL annotations on Windows

[smeenai]

Summary

__declspec(dllexport) and __declspec(dllimport) should only be used
when building libc++abi as a DLL, but that's the more common use case,
so default to adding the annotations and add an option to opt out.

Similar to r282449, which made the corresponding change for libc++.

[EricWF]

LGTM after addressing inline comments. Unfortunately libc++abi doesn't have a way to make _LIBCXXABI_DISABLE_DLL_IMPORT_EXPORT persistent, but this solution works for now.

CMakeLists.txt

255

We probably want to define _LIBCXXABI_DISABLE_DLL_IMPORT_EXPORT on Windows when LIBCXXABI_ENABLE_SHARED=OFF and LIBCXXABI_ENABLE_STATIC=ON.

[smeenai]

Addressing @EricWF's comment

CMakeLists.txt

if (LIBCXXABI_HAS_NOSTDINCXX_FLAG)
   string(REPLACE "-stdlib=libc++" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
   string(REPLACE "-stdlib=libstdc++" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
 endif()
 
 if (LIBCXXABI_USE_COMPILER_RT)
   list(APPEND LIBCXXABI_LINK_FLAGS "-rtlib=compiler-rt")
 endif()
 
+# Let the library headers know they are currently being used to build the
+# library.
+add_definitions(-D_LIBCXXABI_BUILDING_LIBRARY)
+
 append_if(LIBCXXABI_COMPILE_FLAGS LIBCXXABI_HAS_WERROR_FLAG -Werror=return-type)
 
 # Get warning flags
 append_if(LIBCXXABI_COMPILE_FLAGS LIBCXXABI_HAS_W_FLAG -W)
 append_if(LIBCXXABI_COMPILE_FLAGS LIBCXXABI_HAS_WALL_FLAG -Wall)
 append_if(LIBCXXABI_COMPILE_FLAGS LIBCXXABI_HAS_WCHAR_SUBSCRIPTS_FLAG -Wchar-subscripts)
 append_if(LIBCXXABI_COMPILE_FLAGS LIBCXXABI_HAS_WCONVERSION_FLAG -Wconversion)
 append_if(LIBCXXABI_COMPILE_FLAGS LIBCXXABI_HAS_WMISMATCHED_TAGS_FLAG -Wmismatched-tags)
if (NOT LIBCXXABI_ENABLE_THREADS)
   endif()
   add_definitions(-D_LIBCXXABI_HAS_NO_THREADS)
 endif()
 
 if (LIBCXXABI_HAS_PTHREAD_API)
   add_definitions(-D_LIBCPP_HAS_THREAD_API_PTHREAD)
 endif()
 
-# This is the _ONLY_ place where add_definitions is called.
 if (MSVC)
   add_definitions(-D_CRT_SECURE_NO_WARNINGS)
 endif()
 
 # Define LIBCXXABI_USE_LLVM_UNWINDER for conditional compilation.
 if (LIBCXXABI_USE_LLVM_UNWINDER OR LLVM_NATIVE_ARCH MATCHES ARM)
   add_definitions(-DLIBCXXABI_USE_LLVM_UNWINDER=1)
 endif()

include/__cxxabi_config.h

 #else
 #define LIBCXXABI_ARM_EHABI 0
 #endif
 
 #if !defined(__has_attribute)
 #define __has_attribute(_attribute_) 0
 #endif
 
-#if defined(_LIBCXXABI_DLL)
- #if defined(cxxabi_EXPORTS)
+#if defined(_WIN32)
+ #if defined(_LIBCXXABI_DISABLE_DLL_IMPORT_EXPORT)
+  #define _LIBCXXABI_HIDDEN
+  #define _LIBCXXABI_DATA_VIS
+  #define _LIBCXXABI_FUNC_VIS
+  #define _LIBCXXABI_TYPE_VIS
+ #elif defined(_LIBCXXABI_BUILDING_LIBRARY)
   #define _LIBCXXABI_HIDDEN
   #define _LIBCXXABI_DATA_VIS __declspec(dllexport)
   #define _LIBCXXABI_FUNC_VIS __declspec(dllexport)
   #define _LIBCXXABI_TYPE_VIS __declspec(dllexport)
  #else
   #define _LIBCXXABI_HIDDEN
   #define _LIBCXXABI_DATA_VIS __declspec(dllimport)
   #define _LIBCXXABI_FUNC_VIS __declspec(dllimport)