[libc++] Create install-stripped targets

[smeenai]

Summary

LLVM is gaining install-*-stripped targets to perform stripped installs,
and in order for this to be useful for install-distribution, all
potential distribution components should have stripped installation
targets. LLVM has a function to create these install targets, but since
we can't use LLVM CMake functions in libc++, let's do it manually.

[smeenai]

Don't add deprecated target names, since clients should be switching over to the new ones.

include/CMakeLists.txt

if (LIBCXX_INSTALL_HEADERS)
   if (NOT CMAKE_CONFIGURATION_TYPES)
     # this target is just needed as a placeholder for the distribution target
     add_custom_target(cxx-headers)
     add_custom_target(install-cxx-headers
                       DEPENDS cxx-headers ${generated_config_deps}
                       COMMAND "${CMAKE_COMMAND}"
                               -DCMAKE_INSTALL_COMPONENT=cxx-headers
                               -P "${CMAKE_BINARY_DIR}/cmake_install.cmake")
+    # Stripping is a no-op for headers
+    add_custom_target(install-cxx-headers-stripped DEPENDS install-cxx-headers)
 
     add_custom_target(libcxx-headers)
     add_custom_target(install-libcxx-headers DEPENDS install-cxx-headers)
   endif()
 
 endif()

lib/CMakeLists.txt

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