treewide: be explicit about dependence on gettext.h

Dozens of files made use of gettext functions, without explicitly
including gettext.h.  This made it more difficult to find which files
could remove a dependence on cache.h.  Make C files explicitly include
gettext.h if they are using it.

However, while compat/fsmonitor/fsm-ipc-darwin.c should also gain an
include of gettext.h, it was left out to avoid conflicting with an
in-flight topic.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 80d05e2..ed89b7e 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -3,6 +3,7 @@
 #include "config.h"
 #include "builtin.h"
 #include "dir.h"
+#include "gettext.h"
 #include "hex.h"
 #include "parse-options.h"
 #include "strvec.h"