Factor out mi_ui_out instantiation logic

When re-reviewing this [1] I noticed that there were two spots encoding
the logic of instantiating an mi_ui_out object based on the interpreter
name ("mi", "mi1", "mi2" or "mi3"):

 - mi_interp::init
 - mi_load_progress

Both encode the logic to choose what the default version is when the
interpreter name is "mi".  I had forgotten the one in mi_load_progress.

Therefore, I propose extracting that logic to a single function.  I
started to add a new overload of mi_out_new, then realized the current
mi_out_new wasn't very useful, being just a thing wrapper around "new
mi_ui_out".  So I ended up with just an mi_out_new function taking the
interp name as parameter.

I ran the gdb.mi tests, and verified manually the behavior (including
the load command).

[1] https://sourceware.org/ml/gdb-patches/2019-01/msg00427.html

gdb/ChangeLog:

	* mi/mi-out.h (mi_out_new): Change parameter to const char *.
	* mi/mi-out.c (mi_out_new): Change parameter to const char *,
	instantiate mi_ui_out based on interpreter name.
	* mi/mi-interp.c (mi_interp::init): Use the new mi_out_new.
	* mi/mi-main.c (mi_load_progress): Likewise.

1 files changed, 2 insertions, 10 deletions

diff --git a/gdb/mi/mi-main.c b/gdb/mi/mi-main.c
index 46bc928..f4e5e48 100644
--- a/gdb/mi/mi-main.c
+++ b/gdb/mi/mi-main.c
@@ -2173,16 +2173,8 @@ mi_load_progress (const char *section_name,
      which means uiout may not be correct.  Fix it for the duration
      of this function.  */
 
-  std::unique_ptr<ui_out> uiout;
-
-  if (current_interp_named_p (INTERP_MI)
-      || current_interp_named_p (INTERP_MI2))
-    uiout.reset (mi_out_new (2));
-  else if (current_interp_named_p (INTERP_MI1))
-    uiout.reset (mi_out_new (1));
-  else if (current_interp_named_p (INTERP_MI3))
-    uiout.reset (mi_out_new (3));
-  else
+  std::unique_ptr<ui_out> uiout (mi_out_new (current_interpreter ()->name ()));
+  if (uiout == nullptr)
     return;
 
   scoped_restore save_uiout