[gdb] Fix warning in foreach_arch selftests

When running the selftests, I run into:
...
$ gdb -q -batch -ex "maint selftest"
  ...
Running selftest execute_cfa_program::aarch64:ilp32.
warning: A handler for the OS ABI "GNU/Linux" is not built into this
configuration of GDB.  Attempting to continue with the default aarch64:ilp32
settings.
...
and likewise for execute_cfa_program::i8086 and
execute_cfa_program::ia64-elf32.

The warning can easily be reproduced outside the selftests by doing:
...
$ gdb -q -batch -ex "set arch aarch64:ilp32"
...
and can be prevented by first doing "set osabi none".

Fix the warning by setting osabi to none while doing selftests that iterate
over all architectures.

Tested on x86_64-linux.

---
 gdb/osabi.c         | 50 ++++++++++++++++++++++++++++++++++++++------------
 gdb/osabi.h         | 13 +++++++++++++
 gdb/selftest-arch.c | 18 +++++++++++++++++-
 3 files changed, 68 insertions(+), 13 deletions(-)

diff --git a/gdb/osabi.c b/gdb/osabi.c
index bbd7635532f..776e62069e5 100644
--- a/gdb/osabi.c
+++ b/gdb/osabi.c
@@ -32,7 +32,7 @@
 #endif
 
 /* State for the "set osabi" command.  */
-static enum { osabi_auto, osabi_default, osabi_user } user_osabi_state;
+static enum gdb_osabi_mode user_osabi_state;
 static enum gdb_osabi user_selected_osabi;
 static const char *gdb_osabi_available_names[GDB_OSABI_INVALID + 3] = {
   "auto",
@@ -595,15 +595,48 @@ generic_elf_osabi_sniffer (bfd *abfd)
   return osabi;
 }
 
+/* See osabi.h.  */
+
+void
+set_osabi (enum gdb_osabi_mode mode, enum gdb_osabi osabi)
+{
+  if (mode == osabi_auto)
+    user_osabi_state = osabi_auto;
+  else if (mode == osabi_default)
+    {
+      user_selected_osabi = GDB_OSABI_DEFAULT;
+      user_osabi_state = osabi_user;
+    }
+  else
+    {
+      user_selected_osabi = osabi;
+      user_osabi_state = osabi_user;
+    }
+
+  /* NOTE: At some point (true multiple architectures) we'll need to be more
+     graceful here.  */
+  gdbarch_info info;
+  if (! gdbarch_update_p (info))
+    internal_error (__FILE__, __LINE__, _("Updating OS ABI failed."));
+}
+
+/* See osabi.h.  */
+
+void
+get_osabi (enum gdb_osabi_mode &mode, enum gdb_osabi &osabi)
+{
+  mode = user_osabi_state;
+  osabi = user_selected_osabi;
+}
+
 static void
 set_osabi (const char *args, int from_tty, struct cmd_list_element *c)
 {
   if (strcmp (set_osabi_string, "auto") == 0)
-    user_osabi_state = osabi_auto;
+    set_osabi (osabi_auto, GDB_OSABI_INVALID);
   else if (strcmp (set_osabi_string, "default") == 0)
     {
-      user_selected_osabi = GDB_OSABI_DEFAULT;
-      user_osabi_state = osabi_user;
+      set_osabi (osabi_default, GDB_OSABI_INVALID);
     }
   else
     {
@@ -615,8 +648,7 @@ set_osabi (const char *args, int from_tty, struct cmd_list_element *c)
 
 	  if (strcmp (set_osabi_string, gdbarch_osabi_name (osabi)) == 0)
 	    {
-	      user_selected_osabi = osabi;
-	      user_osabi_state = osabi_user;
+	      set_osabi (osabi_user, osabi);
 	      break;
 	    }
 	}
@@ -625,12 +657,6 @@ set_osabi (const char *args, int from_tty, struct cmd_list_element *c)
 			_("Invalid OS ABI \"%s\" passed to command handler."),
 			set_osabi_string);
     }
-
-  /* NOTE: At some point (true multiple architectures) we'll need to be more
-     graceful here.  */
-  gdbarch_info info;
-  if (! gdbarch_update_p (info))
-    internal_error (__FILE__, __LINE__, _("Updating OS ABI failed."));
 }
 
 static void
diff --git a/gdb/osabi.h b/gdb/osabi.h
index be016732cbc..3737a77d50e 100644
--- a/gdb/osabi.h
+++ b/gdb/osabi.h
@@ -50,6 +50,13 @@ enum gdb_osabi
   GDB_OSABI_INVALID		/* keep this last */
 };
 
+enum gdb_osabi_mode
+{
+  osabi_auto,
+  osabi_default,
+  osabi_user
+};
+
 /* Register an OS ABI sniffer.  Each arch/flavour may have more than
    one sniffer.  This is used to e.g. differentiate one OS's a.out from
    another.  The first sniffer to return something other than
@@ -89,4 +96,10 @@ const char *osabi_triplet_regexp (enum gdb_osabi osabi);
 void generic_elf_osabi_sniff_abi_tag_sections (bfd *, asection *,
 					       enum gdb_osabi *);
 
+/* Set osabi to MODE/OSABI.  */
+extern void set_osabi (enum gdb_osabi_mode mode, enum gdb_osabi osabi);
+
+/* Return current osabi setting in MODE/OSABI.  */
+extern void get_osabi (enum gdb_osabi_mode &mode, enum gdb_osabi &osabi);
+
 #endif /* OSABI_H */
diff --git a/gdb/selftest-arch.c b/gdb/selftest-arch.c
index f434da718d5..a4d9de5a74d 100644
--- a/gdb/selftest-arch.c
+++ b/gdb/selftest-arch.c
@@ -66,12 +66,28 @@ foreach_arch_test_generator (const std::string &name,
       auto test_fn
 	= ([=] ()
 	   {
+	     /* Prevent warnings when setting architecture with current osabi
+		settings, like:
+		  A handler for the OS ABI "GNU/Linux" is not built into this
+		  configuration of GDB.  Attempting to continue with the
+		  default aarch64:ilp32 settings.  */
+	     enum gdb_osabi_mode mode;
+	     enum gdb_osabi osabi;
+	     get_osabi (mode, osabi);
+
+	     set_osabi (osabi_user, GDB_OSABI_NONE);
+	     SCOPE_EXIT
+	       {
+		 reset ();
+		 set_osabi (mode, osabi);
+	       };
+
 	     struct gdbarch_info info;
 	     info.bfd_arch_info = bfd_scan_arch (arch);
 	     struct gdbarch *gdbarch = gdbarch_find_by_info (info);
 	     SELF_CHECK (gdbarch != NULL);
+
 	     function (gdbarch);
-	     reset ();
 	   });
 
       tests.emplace_back (string_printf ("%s::%s", name.c_str (), arch),