Make "show remote exec-file" inferior-aware

The "set remote exec-file" setting is per-inferior, but the "show
remote exec-file" command always shows the last set exec-file,
irrespective of the current inferior.  E.g.:

 # Set inferior 1's exec-file:
 (gdb) set remote exec-file prog1

 # Add inferior 2, switch to it, and set its exec-file:
 (gdb) add-inferior
 Added inferior 2
 (gdb) inferior 2
 (gdb) set remote exec-file prog2

 # Switch back to inferior 1, and show its exec-file:
 (gdb) inferior 1
 (gdb) show remote exec-file
 prog2
 ^^^^^ should show "prog1" instead here.

gdb/ChangeLog:
2020-01-10  Pedro Alves  <palves@redhat.com>

	* remote.c (show_remote_exec_file): Show the current inferior's
	exec-file instead of the command variable's value.

gdb/testsuite/ChangeLog:
2020-01-10  Pedro Alves  <palves@redhat.com>

	* gdb.base/remote-exec-file.exp: New file.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2020-01-10  Pedro Alves  <palves@redhat.com>
+
+	* remote.c (show_remote_exec_file): Show the current inferior's
+	exec-file instead of the command variable's value.
+
 2020-01-10  Pedro Alves  <palves@redhat.com>
 
 	* record-full.c (record_full_resume_ptid): New global.

gdb/remote.c

@@ -1268,7 +1268,7 @@ static void
 show_remote_exec_file (struct ui_file *file, int from_tty,
 		       struct cmd_list_element *cmd, const char *value)
 {
-  fprintf_filtered (file, "%s\n", remote_exec_file_var);
+  fprintf_filtered (file, "%s\n", get_remote_exec_file ());
 }
 
 static int

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2020-01-10  Pedro Alves  <palves@redhat.com>
+
+	* gdb.base/remote-exec-file.exp: New file.
+
 2020-01-10  Pedro Alves  <palves@redhat.com>
 
 	* gdb.base/fork-running-state.exp (do_test): Adjust expected

gdb/testsuite/gdb.base/remote-exec-file.exp

@@ -0,0 +1,46 @@
+# Copyright 2019-2020 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Check that "show remote exec-file" displays each inferior's
+# exec-file.  Regression test for a bug where "show remote exec-file"
+# would show the last exec-file set, irrespective of the current
+# inferior.
+
+clean_restart
+
+# Set remote exec-file in inferior 1.
+with_test_prefix "set inf 1" {
+    gdb_test_no_output "set remote exec-file prog1"
+}
+
+# Set remote exec-file in inferior 2.
+with_test_prefix "set inf 2" {
+    gdb_test "add-inferior" "Added inferior 2" "add inferior 2"
+    gdb_test "inferior 2" "Switching to inferior 2.*"
+    gdb_test_no_output "set remote exec-file prog2"
+}
+
+# Check that "show remote exec-file" diplays each inferior's
+# exec-file.
+
+with_test_prefix "show inf 1" {
+    gdb_test "inferior 1" "Switching to inferior 1.*"
+    gdb_test "show remote exec-file" "prog1"
+}
+
+with_test_prefix "show inf 2" {
+    gdb_test "inferior 2" "Switching to inferior 2.*"
+    gdb_test "show remote exec-file" "prog2"
+}