treewide: remove unnecessary inclusions of parse-options.h from headers

The headers 'diagnose.h', 'list-objects-filter-options.h',
'ref-filter.h' and 'remote.h' declare option parsing callback
functions with a 'struct option*' parameter, and 'revision.h' declares
an option parsing helper function taking 'struct parse_opt_ctx_t*' and
'struct option*' parameters.  These headers all include
'parse-options.h', although they don't need any of the type
definitions from that header file.  Furthermore,
'list-objects-filter-options.h' and 'ref-filter.h' also define some
OPT_* macros to initialize a 'struct option', but these don't
necessitate the inclusion of parse-options.h in these headers either,
because these macros are only expanded in source files.

Remove these unnecessary inclusions of parse-options.h and use forward
declarations to declare the necessary types.

After this patch none of the header files include parse-options.h
anymore.

With these changes, the build time after modifying only
parse-options.h is reduced by about 30%, and the number of targets
built is almost 20% less:

  Before:

    $ touch parse-options.h && time make -j4 |wc -l
    353

    real    1m1.527s
    user    3m32.205s
    sys	    0m15.903s

  After:

    289

    real    0m39.285s
    user    2m12.540s
    sys     0m11.164s

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diagnose.h

@@ -2,7 +2,8 @@
 #define DIAGNOSE_H
 
 #include "strbuf.h"
-#include "parse-options.h"
+
+struct option;
 
 enum diagnose_mode {
 	DIAGNOSE_NONE,

list-objects-filter-options.h

@@ -2,9 +2,10 @@
 #define LIST_OBJECTS_FILTER_OPTIONS_H
 
 #include "cache.h"
-#include "parse-options.h"
 #include "string-list.h"
 
+struct option;
+
 /*
  * The list of defined filters for list-objects.
  */

ref-filter.h

@@ -4,7 +4,6 @@
 #include "oid-array.h"
 #include "refs.h"
 #include "commit.h"
-#include "parse-options.h"
 
 /* Quoting styles */
 #define QUOTE_NONE 0
@@ -24,6 +23,7 @@
 
 struct atom_value;
 struct ref_sorting;
+struct option;
 
 enum ref_sorting_order {
 	REF_SORTING_REVERSE = 1<<0,

remote.h

@@ -2,10 +2,10 @@
 #define REMOTE_H
 
 #include "cache.h"
-#include "parse-options.h"
 #include "hashmap.h"
 #include "refspec.h"
 
+struct option;
 struct transport_ls_refs_options;
 
 /**

revision.h

@@ -2,7 +2,6 @@
 #define REVISION_H
 
 #include "commit.h"
-#include "parse-options.h"
 #include "grep.h"
 #include "notes.h"
 #include "pretty.h"
@@ -61,6 +60,8 @@ struct string_list;
 struct saved_parents;
 struct bloom_key;
 struct bloom_filter_settings;
+struct option;
+struct parse_opt_ctx_t;
 define_shared_commit_slab(revision_sources, char *);
 
 struct rev_cmdline_info {