Remove legacy CMake targets for libcxx and libcxxabi

[ldionne]

Summary

We've been meaning to remove those targets for a while, and the fix is
simple enough cause they're all just aliases to other targets.

There's no doubt this commit will break some CI systems, however the
fix is trivial.

[phosek]

LGTM

[ldionne]

Just to clear things out since the review groups are new, I'm still waiting for a thumbs up from someone from the libc++ group (so @EricWF or @mclow.lists).

libcxx/docs/BuildingLibcxx.rst

.. code-block:: bash
   $ cd where-you-want-to-build
   $ mkdir build && cd build
   $ export CC=clang CXX=clang++
   $ cmake -DLLVM_PATH=path/to/separate/llvm \
           -DLIBCXX_CXX_ABI=libcxxabi \
           -DLIBCXX_CXX_ABI_INCLUDE_PATHS=path/to/separate/libcxxabi/include \
           path/to/llvm-project/libcxx
   $ make
-  $ make check-libcxx # optional
+  $ make check-cxx # optional
 
 
 Experimental Support for Windows
 --------------------------------
 
 The Windows support requires building with clang-cl as cl does not support one
 required extension: `#include_next`.  Furthermore, VS 2015 or newer (19.00) is
 required.  In the case of clang-cl, we need to specify the "MS Compatibility

libcxx/docs/TestingLibcxx.rst

 ==============
 Testing libc++
 ==============
 
 .. contents::
   :local:
 
 Getting Started
 ===============
 
-libc++ uses LIT to configure and run its tests. 
+libc++ uses LIT to configure and run its tests.
 
-The primary way to run the libc++ tests is by using `make check-libcxx`. 
+The primary way to run the libc++ tests is by using `make check-cxx`.
 
 However since libc++ can be used in any number of possible
 configurations it is important to customize the way LIT builds and runs
 the tests. This guide provides information on how to use LIT directly to
 test libc++.
 
 Please see the `Lit Command Guide`_ for more information about LIT.
 

libcxx/include/CMakeLists.txt

if (LIBCXX_INSTALL_HEADERS)
   if (NOT CMAKE_CONFIGURATION_TYPES)
     add_custom_target(install-${CXX_HEADER_TARGET}
                       DEPENDS ${CXX_HEADER_TARGET} ${generated_config_deps}
                       COMMAND "${CMAKE_COMMAND}"
                               -DCMAKE_INSTALL_COMPONENT=${CXX_HEADER_TARGET}
                               -P "${CMAKE_BINARY_DIR}/cmake_install.cmake")
     # Stripping is a no-op for headers
     add_custom_target(install-${CXX_HEADER_TARGET}-stripped DEPENDS install-${CXX_HEADER_TARGET})
-
-    add_custom_target(install-libcxx-headers DEPENDS install-${CXX_HEADER_TARGET})
-    add_custom_target(install-libcxx-headers-stripped DEPENDS install-${CXX_HEADER_TARGET}-stripped)
   endif()
 endif()

libcxx/src/CMakeLists.txt

if (NOT CMAKE_CONFIGURATION_TYPES AND (LIBCXX_INSTALL_LIBRARY OR
     add_custom_target(install-cxx-stripped
                       DEPENDS ${lib_install_target}
                               ${experimental_lib_install_target}
                               ${header_install_target}
                       COMMAND "${CMAKE_COMMAND}"
                       -DCMAKE_INSTALL_COMPONENT=cxx
                       -DCMAKE_INSTALL_DO_STRIP=1
                       -P "${LIBCXX_BINARY_DIR}/cmake_install.cmake")
-    add_custom_target(install-libcxx DEPENDS install-cxx)
 endif()

libcxx/test/CMakeLists.txt

if (LIBCXX_INCLUDE_TESTS)
   configure_lit_site_cfg(
     ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.in
     ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg)
 
   add_lit_testsuite(check-cxx
     "Running libcxx tests"
     ${CMAKE_CURRENT_BINARY_DIR}
     DEPENDS cxx ${LIBCXX_TEST_DEPS})
-
-  add_custom_target(check-libcxx DEPENDS check-cxx)
 endif()
 
 if (LIBCXX_GENERATE_COVERAGE)
   include(CodeCoverage)
   set(output_dir "${CMAKE_CURRENT_BINARY_DIR}/coverage")
   set(capture_dirs
       "${LIBCXX_LIB_CMAKEFILES_DIR}/cxx_objects.dir/"
       "${LIBCXX_LIB_CMAKEFILES_DIR}/cxx.dir/"

libcxxabi/src/CMakeLists.txt

COMMAND "${CMAKE_COMMAND}"
             -DCMAKE_INSTALL_COMPONENT=cxxabi
             -P "${LIBCXXABI_BINARY_DIR}/cmake_install.cmake")
   add_custom_target(install-cxxabi-stripped
     DEPENDS cxxabi
     COMMAND "${CMAKE_COMMAND}"
             -DCMAKE_INSTALL_COMPONENT=cxxabi
             -DCMAKE_INSTALL_DO_STRIP=1
             -P "${LIBCXXABI_BINARY_DIR}/cmake_install.cmake")
-
-  # TODO: This is a legacy target name and should be removed at some point.
-  add_custom_target(install-libcxxabi DEPENDS install-cxxabi)
 endif()

libcxxabi/test/CMakeLists.txt

 configure_lit_site_cfg(
   ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.in
   ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg)
 
 add_lit_testsuite(check-cxxabi "Running libcxxabi tests"
   ${CMAKE_CURRENT_BINARY_DIR}
   DEPENDS ${LIBCXXABI_TEST_DEPS}
   )
-
-# TODO: This is a legacy target name and should be removed at some point.
-add_custom_target(check-libcxxabi DEPENDS check-cxxabi)