[libc++abi] Add install-cxxabi-stripped target

[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++abi, let's do it manually.

[beanz]

LGTM.

libcxxabi/trunk/src/CMakeLists.txt

 endif()
 
 if (NOT CMAKE_CONFIGURATION_TYPES AND LIBCXXABI_INSTALL_LIBRARY)
   add_custom_target(install-cxxabi
     DEPENDS cxxabi
     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()