kbuild: error out on missing MODULE_LICENSE

Adrian Bunk suggested a build time check for
missing MODULE_LICENSE annotation in modules.
The build time check is fatal as we really
want this fixed for all modules.
In-tree modules should all have been fixed up by now.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Adrian Bunk <bunk@kernel.org>

scripts/mod/modpost.c

@@ -1552,6 +1552,10 @@ static void read_symbols(char *modname)
 	}
 
 	license = get_modinfo(info.modinfo, info.modinfo_len, "license");
+	if (!license && !is_vmlinux(modname))
+		fatal("modpost: missing MODULE_LICENSE() in %s\n"
+		      "see include/linux/module.h for "
+		      "more information\n", modname);
 	while (license) {
 		if (license_is_gpl_compatible(license))
 			mod->gpl_compatible = 1;