genksyms: Do not expand internal types

Consider structures, unions and enums defined in the source file as
internal and do not expand them. This way, changes to e.g. struct
serial_private in drivers/tty/serial/8250_pci.c will not affect the
checksum of the pciserial_* exports.
diff --git a/scripts/genksyms/genksyms.h b/scripts/genksyms/genksyms.h
index 7ec52ae..3bffdca 100644
--- a/scripts/genksyms/genksyms.h
+++ b/scripts/genksyms/genksyms.h
@@ -37,6 +37,7 @@
 struct string_list {
 	struct string_list *next;
 	enum symbol_type tag;
+	int in_source_file;
 	char *string;
 };
 
@@ -57,7 +58,8 @@
 #define YYSTYPE yystype
 
 extern int cur_line;
-extern char *cur_filename;
+extern char *cur_filename, *source_file;
+extern int in_source_file;
 
 struct symbol *find_symbol(const char *name, enum symbol_type ns, int exact);
 struct symbol *add_symbol(const char *name, enum symbol_type type,