Flymake highlights GCC info/notes as detected by flymake-proc.el

Flymake highlights GCC info/notes as detected by flymake-proc.el

* lisp/progmodes/flymake-proc.el
(flymake-proc--diagnostics-for-pattern): Rewrite (using cl-loop) to
honour more sophisticated flymake-proc-diagnostic-type-pred.
(flymake-warning-re): Is now an obsolete alias for
flymake-proc-diagnostic-type-pred.
(flymake-proc-diagnostic-type-pred): Rename and augment from
flymake-proc-warning-predicate.  (flymake-proc-warning-predicate):
Delete.

* lisp/progmodes/flymake.el (flymake-note): New face.
(flymake-diagnostic-types-alist): Simplify.
(flymake-note): New overlay category.
(flymake--lookup-type-property): Only lookup single keys, not lists.
(flymake--diag-errorp): Rewrite.
(flymake--highlight-line): Use flymake--lookup-type-property.

* test/lisp/progmodes/flymake-tests.el
(different-diagnostic-types): Rename from errors-and-warnings.
Check notes.
(flymake-tests--call-with-fixture): Use
flymake-proc-diagnostic-type-pred.