These redirecting makefiles simplifies compiling from some editors and
when CWD is not the root of the source tree. This is similar to what was
introduced in systemd in 340d89e ("build-sys: add small redirecting
Makefiles to simplify compilation from within emacs")
Add kmod-* prefixed tool names, add 'tags' in root directory (for ctags,
matches cscope.out ignore already in there), and prefix tools/ entries
with '/' so they are absolute ignores and don't apply to subdirectories.
