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'.