use language of the main symbol

With "dwz -m", "main" appears in both the PU and the importing CU when
running anon-struct.exp.  However, the PU does not have a file name.
So, find_main_filename returns the empty string, making
deduce_language_from_filename return language_unknown.

This patch fixes this problem by changing gdb to use the ordinary
symbol-lookup functions to find "main"'s symbol.  Then, it examines the
symbol's language.

I think this is cleaner than the current approach.  For one thing it
avoids trying to guess the language based on the source file name,
instead deferring to the presumably more reliable debuginfo.

Another possible fix would have been to change how the file name is
found via the "qf" methods.  However, I think the approach given is
preferable for the reason outlined above.

This required a minor test suite change, as now a symtab is expanded
during the search for "main".

Built and regtested (both ways) on x86-64 Fedora 18.

	* symfile.c (set_initial_language): Look up "main" symbol
	and use its language.
	* symtab.c (find_main_filename): Remove.
	* symtab.h (find_main_filename): Remove.

	* gdb.base/maint.exp: Allow zero symtabs to be expanded.

1 files changed, 4 insertions, 4 deletions

diff --git a/gdb/symfile.c b/gdb/symfile.c
index 3328648..3dd5509 100644
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -1612,11 +1612,11 @@ set_initial_language (void)
     lang = language_of_main;
   else
     {
-      const char *filename;
+      char *name = main_name ();
+      struct symbol *sym = lookup_symbol (name, NULL, VAR_DOMAIN, NULL);
 
-      filename = find_main_filename ();
-      if (filename != NULL)
-	lang = deduce_language_from_filename (filename);
+      if (sym != NULL)
+	lang = SYMBOL_LANGUAGE (sym);
     }
 
   if (lang == language_unknown)