lib: save a bit of space with some structure packing

- Reorder some internal struct members so that less padding is used.

This is an attempt at saving a bit of space by packing some structs
(using pahole to find the holes) where it might make sense to do
so without losing readability.

I.e., I tried to avoid separating fields that seem grouped
together (like the cwd... fields in struct ftp_conn for instance).
Also abstained from touching fields behind conditional macros as
that quickly can get complicated.

Closes https://github.com/curl/curl/pull/6483

lib/formdata.h

@@ -29,22 +29,22 @@
 /* used by FormAdd for temporary storage */
 struct FormInfo {
   char *name;
-  bool name_alloc;
   size_t namelength;
   char *value;
-  bool value_alloc;
   curl_off_t contentslength;
   char *contenttype;
-  bool contenttype_alloc;
   long flags;
   char *buffer;      /* pointer to existing buffer used for file upload */
   size_t bufferlength;
   char *showfilename; /* The file name to show. If not set, the actual
                          file name will be used */
-  bool showfilename_alloc;
   char *userp;        /* pointer for the read callback */
   struct curl_slist *contentheader;
   struct FormInfo *more;
+  bool name_alloc;
+  bool value_alloc;
+  bool contenttype_alloc;
+  bool showfilename_alloc;
 };
 
 CURLcode Curl_getformdata(struct Curl_easy *data,