emacs: also handle paths like "..\chrome/foo/bar" seen in build output

tools/emacs/trybot.el

Index: tools/emacs/trybot.el
diff --git a/tools/emacs/trybot.el b/tools/emacs/trybot.el
index 2c658976f06001388e10fdb5e292ad56c370602f..970ffc085d9447d2f50ab5211533b9af5f047c4c 100644
--- a/tools/emacs/trybot.el
+++ b/tools/emacs/trybot.el
@@ -45,7 +45,15 @@
 
   ; Fix Windows paths ("d:\...\src\").
   (save-excursion
-    (while (re-search-forward "\\(^.:\\\\.*\\\\src\\\\\\)\\(.*?\\)[(:]" nil t)
+    ; This regexp is subtle and rather hard to read. :~(
+    ; Use regexp-builder when making changes to it.
+    (while (re-search-forward
+            (concat
+             ; First part: path leader, either of the form
+             ;   e:\...src\  or  ..\
+             "\\(^.:\\\\.*\\\\src\\\\\\|\\.\\.\\\\\\)"
+             ; Second part: path, followed by error message marker.
+             "\\(.*?\\)[(:]") nil t)
       (replace-match "" nil t nil 1)
       ; Line now looks like:
       ;  foo\bar\baz.cc error message here