switch to clang-format-3.8 (#2547)

https://llvm.org/bugs/show_bug.cgi?id=30353 was filed for the unintended
line break between in e.g. “TAILQ_ENTRY(foo)\nbar;”.

Until that’s fixed or a workaround is known, we’ll live with line
breaks. To make it a bit easier for readers to see what’s going on, I
added extra line breaks around each such struct member/variable
definition, so that they at least visually are a single unit.

fixes #2174

src/commands.c

@@ -142,7 +142,9 @@ static Con *maybe_auto_back_and_forth_workspace(Con *workspace) {
  */
 typedef struct owindow {
     Con *con;
-    TAILQ_ENTRY(owindow) owindows;
+
+    TAILQ_ENTRY(owindow)
+    owindows;
 } owindow;
 
 typedef TAILQ_HEAD(owindows_head, owindow) owindows_head;