merge-ort: prevent the_repository from coming back

There are two things preventing us from removing our usage of
USE_THE_REPOSITORY_VARIABLE: one necessary use of the_repository in
prefetch_for_content_merges(), and the use of DEFAULT_ABBREV.  We have
removed all other uses of the_repository in merge-ort before (multiple
times), but without removing that definition, they keep coming back.

Define the_repository to make it a compilation error so that they don't
come back any more, with a special carve-out for
prefetch_for_content_merges().

Signed-off-by: Elijah Newren <newren@gmail.com>

Author: newren

merge-ort.c

@@ -53,6 +53,8 @@
 #include "unpack-trees.h"
 #include "xdiff-interface.h"
 
+#define the_repository DO_NOT_USE_THE_REPOSITORY
+
 /*
  * We have many arrays of size 3.  Whenever we have such an array, the
  * indices refer to one of the sides of the three-way merge.  This is so
@@ -4433,6 +4435,8 @@ static int process_entry(struct merge_options *opt,
 	return 0;
 }
 
+#undef the_repository
+
 static void prefetch_for_content_merges(struct merge_options *opt,
 					struct string_list *plist)
 {
@@ -4481,6 +4485,8 @@ static void prefetch_for_content_merges(struct merge_options *opt,
 	oid_array_clear(&to_fetch);
 }
 
+#define the_repository DO_NOT_USE_the_repository
+
 static int process_entries(struct merge_options *opt,
 			   struct object_id *result_oid)
 {