Reapply "[libc++abi] Stop copying headers to the build directory"

This was needed before #115077
since the compiler-rt test build made assumptions about the build
layout of libc++ and libc++abi, but now they link against a local
installation of these libraries so we no longer need this workaround.

The last attempt at landing this was reverted due to buildbot failures
which should be fixed by llvm/llvm-zorg#299.

Pull Request: #115379

libcxxabi/CMakeLists.txt

@@ -86,12 +86,6 @@ set(LIBCXXABI_STATIC_OUTPUT_NAME "c++abi" CACHE STRING "Output name for the stat
 
 set(LIBCXXABI_INSTALL_INCLUDE_DIR "${CMAKE_INSTALL_INCLUDEDIR}/c++/v1" CACHE STRING "Path to install the libc++abi headers at.")
 
-if(LLVM_LIBRARY_OUTPUT_INTDIR)
-  set(LIBCXXABI_GENERATED_INCLUDE_DIR "${LLVM_BINARY_DIR}/include/c++/v1")
-else()
-  set(LIBCXXABI_GENERATED_INCLUDE_DIR "${CMAKE_BINARY_DIR}/include/c++/v1")
-endif()
-
 set(LIBCXXABI_LIBCXX_LIBRARY_PATH "" CACHE PATH "The path to libc++ library.")
 set(LIBCXXABI_LIBRARY_VERSION "1.0" CACHE STRING
 "Version of libc++abi. This will be reflected in the name of the shared \

libcxxabi/include/CMakeLists.txt

@@ -3,20 +3,7 @@ set(files
   cxxabi.h
   )
 
-foreach(f ${files})
-  set(src "${CMAKE_CURRENT_SOURCE_DIR}/${f}")
-  set(dst "${LIBCXXABI_GENERATED_INCLUDE_DIR}/${f}")
-  add_custom_command(OUTPUT ${dst}
-    DEPENDS ${src}
-    COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
-    COMMENT "Copying CXXABI header ${f}")
-  list(APPEND _all_includes "${dst}")
-endforeach()
-
-add_custom_target(generate-cxxabi-headers ALL DEPENDS ${_all_includes})
-
 add_library(cxxabi-headers INTERFACE)
-add_dependencies(cxxabi-headers generate-cxxabi-headers)
 target_include_directories(cxxabi-headers INTERFACE "${CMAKE_CURRENT_SOURCE_DIR}")
 
 if (LIBCXXABI_INSTALL_HEADERS)