build: split libmultiprocess subtree

cmake/libmultiprocess.cmake

@@ -29,10 +29,4 @@ function(add_libmultiprocess subdir)
     # Add tests to "all" target so ctest can run them
     set_target_properties(mptest PROPERTIES EXCLUDE_FROM_ALL OFF)
   endif()
-  # Exclude examples from compilation database, because the examples are not
-  # built by default, and they contain generated c++ code. Without this
-  # exclusion, tools like clang-tidy and IWYU that make use of compilation
-  # database would complain that the generated c++ source files do not exist. An
-  # alternate fix could build "mpexamples" by default like "mptests" above.
-  set_target_properties(mpcalculator mpprinter mpexample PROPERTIES EXPORT_COMPILE_COMMANDS OFF)
 endfunction()

doc/developer-notes.md

@@ -1136,9 +1136,15 @@ To update the subtree:
 
 ```sh
 git fetch libmultiprocess
-git subtree pull --prefix=src/ipc/libmultiprocess libmultiprocess master --squash
+git subtree pull --prefix=src/ipc/libmultiprocess libmultiprocess lib --squash
 ```
 
+The `lib` branch is published by libmultiprocess upstream and contains
+only the files needed to do a full build (regular and via `depends`). It
+is produced from `master` with `git subtree split --prefix=lib`; CI
+scripts, documentation, and other upstream-only files are intentionally
+excluded from the subtree.
+
 The ultimate upstream of the few externally managed subtrees are:
 
 - src/leveldb