symlink -- A build check method that checks if target points to dependency.
build_check symlink
The symlink method will only execute the action if the target is not a symlink to the dependency. It is exactly like the exact_match method when it comes to repositories or build_cache. For example,
$(ROOT)/include/%.h : %.h : build_check symlink
&ln -fr $(input) $(output)
publishes a file, but does not repeat this when the file changes (i.e. a generated header).
