Show number of errors in compilation-mode mode-line

Show number of errors in compilation-mode mode-line

Bug#25354
* lisp/progmodes/compile.el (compilation-num-errors-found): Provide
default value.
(compilation-num-warnings-found, compilation-num-infos-found): New
defvars.
(compilation-mode-line-errors): New defconst.
(compilation-face): Remove.
(compilation-type, compilation--note-type): New functions.
(compilation-parse-errors): Call compilation--note-type.
(compilation-start): Include compilation-mode-line-errors in
mode-line-process.
(compilation-setup): Initialize compilation-num-* variables to 0.
(compilation-handle-exit): Include compilation-mode-line-errors in
mode-line-process.
* doc/emacs/building.texi (Compilation): Document new feature.