Add another constructor to scoped_restore_current_language

While working on something else, I noticed that this is relatively
common:

  scoped_restore_current_language save;
  set_language (something);

This patch adds a second constructor to
scoped_restore_current_language to simplify this idiom.

Reviewed-By: Tom de Vries <tdevries@suse.de>

gdb/breakpoint.c

@@ -3734,8 +3734,7 @@ create_std_terminate_master_breakpoint (void)
   const char *const func_name = "std::terminate()";
 
   scoped_restore_current_program_space restore_pspace;
-  scoped_restore_current_language save_language;
-  set_language (language_cplus);
+  scoped_restore_current_language save_language (language_cplus);
 
   for (struct program_space *pspace : program_spaces)
     {

gdb/language.c

@@ -110,6 +110,13 @@ scoped_restore_current_language::scoped_restore_current_language ()
 {
 }
 
+scoped_restore_current_language::scoped_restore_current_language
+    (enum language lang)
+  : scoped_restore_current_language ()
+{
+  set_language (lang);
+}
+
 scoped_restore_current_language::~scoped_restore_current_language ()
 {
   /* If both are NULL, then that means dont_restore was called.  */

gdb/language.h

@@ -860,6 +860,10 @@ class scoped_restore_current_language
 public:
 
   scoped_restore_current_language ();
+
+  /* Set the current language as well.  */
+  explicit scoped_restore_current_language (enum language lang);
+
   ~scoped_restore_current_language ();
 
   scoped_restore_current_language (scoped_restore_current_language &&other)

gdb/mi/mi-main.c

@@ -2130,10 +2130,7 @@ mi_cmd_execute (struct mi_parse *parse)
 
   std::optional<scoped_restore_current_language> lang_saver;
   if (parse->language != language_unknown)
-    {
-      lang_saver.emplace ();
-      set_language (parse->language);
-    }
+    lang_saver.emplace (parse->language);
 
   current_context = parse;
 

gdb/parse.c

@@ -423,8 +423,7 @@ parse_exp_in_context (const char **stringptr, CORE_ADDR pc,
 		   expression_context_pc, flags, *stringptr,
 		   completer != nullptr, tracker);
 
-  scoped_restore_current_language lang_saver;
-  set_language (lang->la_language);
+  scoped_restore_current_language lang_saver (lang->la_language);
 
   try
     {
@@ -490,10 +489,7 @@ parse_expression_with_language (const char *string, enum language lang)
 {
   std::optional<scoped_restore_current_language> lang_saver;
   if (current_language->la_language != lang)
-    {
-      lang_saver.emplace ();
-      set_language (lang);
-    }
+    lang_saver.emplace (lang);
 
   return parse_expression (string);
 }

gdb/symmisc.c

@@ -366,8 +366,7 @@ dump_symtab (struct symtab *symtab, struct ui_file *outfile)
      But use only real languages, not placeholders.  */
   if (symtab->language () != language_unknown)
     {
-      scoped_restore_current_language save_lang;
-      set_language (symtab->language ());
+      scoped_restore_current_language save_lang (symtab->language ());
       dump_symtab_1 (symtab, outfile);
     }
   else