compile.el contains this line:
 
       (: "[ skipping " (+ ".") " ]")
 
I think this should be:
 
       (: "[ skipping " (+ (regexp ".")) " ]")
 
A typical error message is:
 
boost/container/detail/flat_tree.hpp:589:25:   [ skipping 5 instantiation contexts, use -ftemplate-backtrace-limit=0 to disable ]
 
This is diagnosed as 'error' and not 'note'.