Revert "Remove legacy CMake targets for libcxx and libcxxabi"

This reverts commit f383fb40b. It looks like several of our build bots
are still using the legacy target names, so we'll change those before
we commit this change again.

GitOrigin-RevId: 04d48111bf932c2beb51784061a41a7938032a4e
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 44aa638..965b1e2 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -295,4 +295,7 @@
             -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()
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index bedfce8..b47eef7 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -81,3 +81,6 @@
   ${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)