[libcxx] Don't generate cxx-abilist for some sets of targets

[lanza]

Summary

Windows didn't previously use this mechanism and the change introduced
in https://reviews.llvm.org/D92194 now is causing it to do so. This
fails on "$<TARGET_SONAME_FILE:cxx_shared>" as this is not available
on Windows. Simply reintroduce the first test that excluded Windows
here.

[ldionne]

Can you please show me how you're configuring your build? Also, what exact error are you seeing?

The goal of D92194 was specifically to get rid of this special logic around the target, so we won't go back. But we might need to use a different way to get to the library file on Windows.

[lanza]

Seems pretty trivially that this just requires LIBCXX_INCLUDE_TESTS and LIBCXX_ENABLE_SHARED for Windows. The error is:

CMake Error at /data/users/lanza/toolchain_dev/external/llvm-project/libcxx/lib/abi/CMakeLists.txt:67 (add_custom_target):
  Error evaluating generator expression:

    $<TARGET_SONAME_FILE:cxx_shared>

  TARGET_SONAME_FILE is not allowed for DLL target platforms.

libcxx/lib/abi/CMakeLists.txt

     message(STATUS "ABI list file not generated for configuration ${abi_list_identifier}, `check-cxx-abilist` will not be available.")
   endif()
 
-  add_custom_target(generate-cxx-abilist
-    COMMAND "${Python3_EXECUTABLE}" "${LIBCXX_SOURCE_DIR}/utils/generate_abi_list.py"
-            --output "${abi_list_file}"
-            "$<TARGET_SONAME_FILE:cxx_shared>"
-    DEPENDS cxx_shared
-    COMMENT "Generating the ABI list file for configuration ${abi_list_identifier}")
+  if ("${LIBCXX_CXX_ABI_LIBNAME}" STREQUAL "libcxxabi" OR
+         (APPLE AND "${LIBCXX_CXX_ABI_LIBNAME}" STREQUAL "default"))
+    add_custom_target(generate-cxx-abilist
+      COMMAND "${Python3_EXECUTABLE}" "${LIBCXX_SOURCE_DIR}/utils/generate_abi_list.py"
+              --output "${abi_list_file}"
+              "$<TARGET_SONAME_FILE:cxx_shared>"
+      DEPENDS cxx_shared
+      COMMENT "Generating the ABI list file for configuration ${abi_list_identifier}")
+  endif()
 else()
   message(STATUS "Not building a shared library for libc++ -- the ABI list targets will not be available.")
 endif()