[C++] remote.c: Avoid enum arithmetic

Fixes:

  src/gdb/remote.c: In function ‘void remote_unpush_target()’:
  src/gdb/remote.c:4610:45: error: invalid conversion from ‘int’ to ‘strata’ [-fpermissive]
     pop_all_targets_above (process_stratum - 1);
					       ^
  In file included from src/gdb/inferior.h:38:0,
		   from src/gdb/remote.c:25:
  src/gdb/target.h:2299:13: error:   initializing argument 1 of ‘void pop_all_targets_above(strata)’ [-fpermissive]
   extern void pop_all_targets_above (enum strata above_stratum);
	       ^

I used to carry a patch in the C++ branch that just did:

 -  pop_all_targets_above (process_stratum - 1);
 +  pop_all_targets_above ((enum strata) (process_stratum - 1));

But then thought that maybe adding a routine that does exactly what we
need results in clearer code.  This is the result.

gdb/ChangeLog:
2015-11-19  Pedro Alves  <palves@redhat.com>

	* remote.c (remote_unpush_target): Use
	pop_all_targets_at_and_above instead of pop_all_targets_above.
	* target.c (unpush_target_and_assert): New function, factored out
	from ...
	(pop_all_targets_above): ... here.
	(pop_all_targets_at_and_above): New function.
	* target.h (pop_all_targets_at_and_above): Declare.

1 files changed, 25 insertions, 11 deletions

diff --git a/gdb/target.c b/gdb/target.c
index 93786c3..0ae6708 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -746,21 +746,35 @@ unpush_target (struct target_ops *t)
   return 1;
 }
 
+/* Unpush TARGET and assert that it worked.  */
+
+static void
+unpush_target_and_assert (struct target_ops *target)
+{
+  if (!unpush_target (target))
+    {
+      fprintf_unfiltered (gdb_stderr,
+			  "pop_all_targets couldn't find target %s\n",
+			  target->to_shortname);
+      internal_error (__FILE__, __LINE__,
+		      _("failed internal consistency check"));
+    }
+}
+
 void
 pop_all_targets_above (enum strata above_stratum)
 {
   while ((int) (current_target.to_stratum) > (int) above_stratum)
-    {
-      if (!unpush_target (target_stack))
-	{
-	  fprintf_unfiltered (gdb_stderr,
-			      "pop_all_targets couldn't find target %s\n",
-			      target_stack->to_shortname);
-	  internal_error (__FILE__, __LINE__,
-			  _("failed internal consistency check"));
-	  break;
-	}
-    }
+    unpush_target_and_assert (target_stack);
+}
+
+/* See target.h.  */
+
+void
+pop_all_targets_at_and_above (enum strata stratum)
+{
+  while ((int) (current_target.to_stratum) >= (int) stratum)
+    unpush_target_and_assert (target_stack);
 }
 
 void