[CMake] Support symlinking runtimes under a different name

[phosek]

Summary

When using the per-target runtimes directory layout with the runtimes
build, this change allows symlinking runtimes under a different target
(triple) name. The example use case is as follow:

set(LLVM_RUNTIME_TARGET_x86_64-linux-gnu_SYMLINK "x86_64-unknown-linux-gnu" CACHE STRING "")

This would create a symlink x86_64-linux-gnu pointing to the
x86_64-unknown-linux-gnu runtime directory.

[smeenai]

This could be useful for us!

From my reading of the code, if you have e.g. armv7-none-linux-androideabi16 in your LLVM_RUNTIME_TARGETS, you could set LLVM_RUNTIME_TARGET_armv7-none-linux-androideabi16_SYMLINK to armv7-none-linux-andrdoieabi and it would create a symlink from armv7-none-linux-androideabi to armv7-none-linux-androideabi16. That's the opposite of what I'm reading in the description (though I think the code makes sense as-is).

llvm/runtimes/CMakeLists.txt

563

Maybe SYMLINKS instead of SYMLINK to reflect that there can be multiple?

584

Use add_llvm_install_targets?

590

Add dependencies for the *-stripped targets too?

[smeenai]

There's also libraries which are installed outside the resource directory, right? E.g. libc++ and libc++abi.

llvm/runtimes/CMakeLists.txt

else()
             CMAKE_ARGS -DLLVM_RUNTIMES_PREFIX=${name}/
                        -DLLVM_RUNTIMES_LIBDIR_SUBDIR=${multilib})
           add_dependencies(runtimes runtimes-${name}+${multilib})
           add_dependencies(runtimes-configure runtimes-${name}+${multilib}-configure)
           add_dependencies(install-runtimes install-runtimes-${name}+${multilib})
           add_dependencies(install-runtimes-stripped install-runtimes-${name}+${multilib}-stripped)
         endforeach()
       endforeach()
+
+      string(REGEX MATCH "[0-9]+\\.[0-9]+(\\.[0-9]+)?" CLANG_VERSION
+             ${PACKAGE_VERSION})
+
+      foreach(name ${LLVM_RUNTIME_TARGETS})
+        foreach(symlink ${LLVM_RUNTIME_TARGET_${name}_SYMLINK})
+          if(CMAKE_HOST_UNIX)
+            set(LLVM_LINK_OR_COPY create_symlink)
+          else()
+            set(LLVM_LINK_OR_COPY copy)
+          endif()
+          set(dst_path ${LLVM_LIBRARY_OUTPUT_INTDIR}/clang/${CLANG_VERSION}/${symlink})
+          add_custom_command(TARGET runtimes-${name} POST_BUILD
+            COMMAND ${CMAKE_COMMAND} -E ${LLVM_LINK_OR_COPY} "${name}" "${dst_path}")
+
+          foreach(path ${CMAKE_MODULE_PATH})
+            if(EXISTS ${path}/LLVMInstallSymlink.cmake)
+              set(INSTALL_SYMLINK ${path}/LLVMInstallSymlink.cmake)
+              break()
+            endif()
+          endforeach()
+
+          install(SCRIPT ${INSTALL_SYMLINK}
+                  CODE "install_symlink(${symlink} ${name} lib${LLVM_LIBDIR_SUFFIX}/clang/${CLANG_VERSION})"
+                  COMPONENT ${symlink})
+
+          add_custom_target(install-runtimes-${symlink}
+                            DEPENDS install-runtimes-${name}
+                            COMMAND "${CMAKE_COMMAND}"
+                                    -DCMAKE_INSTALL_COMPONENT="${symlink}"
+                                    -P "${CMAKE_BINARY_DIR}/cmake_install.cmake"
+                            USES_TERMINAL)
+          add_dependencies(install-runtimes install-runtimes-${symlink})
+        endforeach()
+      endforeach()
     endif()
 
     if(NOT LLVM_BUILD_INSTRUMENTED AND CLANG_ENABLE_BOOTSTRAP)
       # TODO: This is a hack needed because the libcxx headers are copied into the
       # build directory during configuration. Without that step the clang in the
       # build directory cannot find the C++ headers in certain configurations.
       # I need to build a mechanism for runtime projects to provide CMake code
       # that executes at LLVM configuration time to handle this case.