misc/emacs: Fix the gofmt patching when the TMPDIR is not the default.

The previous code assumed the gofmt output referred to /tmp but
that's not true if TMPDIR points somewhere else (like on Macs).
Fixes #3782.

R=sameer
CC=golang-dev
https://golang.org/cl/6346050

misc/emacs/go-mode.el

@@ -820,7 +820,10 @@ Replace the current buffer on success; display errors on failure."
   ;; apply all the patch hunks
   (with-current-buffer patchbuf
     (goto-char (point-min))
-    (if (re-search-forward "^--- \\(/tmp/gofmt[0-9]*\\)" nil t)
+    ;; The .* is for TMPDIR, but to avoid dealing with TMPDIR
+    ;; having a trailing / or not, it's easier to just search for .*
+    ;; especially as we're only replacing the first instance.
+    (if (re-search-forward "^--- \\(.*/gofmt[0-9]*\\)" nil t)
       (replace-match filename nil nil nil 1))
     (condition-case nil
         (while t