build: add clang-cl and clang++ symlinks in the build tree

[compnerd]

Summary

This adds the clang-cl and clang++ symlinks. Since there are no targets to depend on for this, we cannot force the creation of the symlinks. Furthermore, the current build only installs the symbolic links in the install tree, not the build tree. This enables the use of the clang driver without having adjust the C/C++ flags to add --driver=... to switch between driver modes. Usage of this is present in Swift and there is some usage in lldb.

[smeenai]

Furthermore, the current build only installs the symbolic links in the install tree, not the build tree

This isn't right ... if I look at my LLVM build tree, I have clang, clang++ and clang-cl symlinks, all pointing to the actual clang-10 binary.

Where are you seeing this?

[compnerd]

I think I must have had something else in my tree, cause a clean build does build them.

tools/driver/CMakeLists.txt

clang_target_link_libraries(clang
   clangBasic
   clangCodeGen
   clangDriver
   clangFrontend
   clangFrontendTool
   clangSerialization
   )
 
+if(CMAKE_VERSION VERSION_GREATER 3.7 OR NOT CMAKE_SYSTEM_NAME STREQUAL Windows)
+  set(command create_symlink)
+else()
+  set(command copy)
+endif()
+add_custom_command(TARGET clang POST_BUILD
+  COMMAND ${CMAKE_COMMAND} -E ${command} $<TARGET_FILE:clang> $<TARGET_FILE_DIR:clang>/clang-cl${CMAKE_EXECUTABLE_SUFFIX}
+  COMMAND ${CMAKE_COMMAND} -E ${command} $<TARGET_FILE:clang> $<TARGET_FILE_DIR:clang>/clang++${CMAKE_EXECUTABLE_SUFFIX})
+
 if(WIN32 AND NOT CYGWIN)
   # Prevent versioning if the buildhost is targeting for Win32.
 else()
   set_target_properties(clang PROPERTIES VERSION ${CLANG_EXECUTABLE_VERSION})
 endif()
 
 # Support plugins.
 if(CLANG_PLUGIN_SUPPORT)