sort and group includes

* includes are sorted alphabetically

* their grouping and layout is the following:
  - nsxiv.h will be the first include
  - followed by any internal headers (e.g "commands.h" "config.h")
  - followed by system headers (<stdlib.h> etc)
  - followed by third party headers (X.h libwebp etc)

* also add `llvm-include-order` check to clang-tidy so that it can catch
  unsorted includes during CI.

1 files changed, 3 insertions, 2 deletions

diff --git a/window.c b/window.c
index 3cfa188..f472474 100644
--- a/window.c
+++ b/window.c
@@ -22,13 +22,14 @@
 #include "config.h"
 #include "icon/data.h"
 
+#include <locale.h>
 #include <stdlib.h>
 #include <string.h>
-#include <locale.h>
 #include <unistd.h>
-#include <X11/cursorfont.h>
+
 #include <X11/Xatom.h>
 #include <X11/Xresource.h>
+#include <X11/cursorfont.h>
 
 #if HAVE_LIBFONTS
 #include "utf8.h"