dl: fix `v -cflags "-Werror" use_test.v`

cmd/tools/vtest-self.v

@@ -35,8 +35,6 @@ const (
 	skip_with_werror              = [
 		'vlib/sync/array_rlock_test.v',
 		'vlib/clipboard/clipboard_test.v',
-		'vlib/dl/dl_test.v',
-		'vlib/dl/example/use_test.v',
 		'vlib/eventbus/eventbus_test.v',
 		'vlib/gx/color_test.v',
 		'vlib/json/json_test.v',

vlib/dl/dl_nix.c.v

@@ -15,7 +15,7 @@ fn C.dlclose(handle voidptr) int
 
 // open loads the dynamic shared object.
 pub fn open(filename string, flags int) voidptr {
-	return C.dlopen(filename.str, flags)
+	return C.dlopen(charptr(filename.str), flags)
 }
 
 // close frees a given shared object.
@@ -25,5 +25,5 @@ pub fn close(handle voidptr) bool {
 
 // sym returns an address of a symbol in a given shared object.
 pub fn sym(handle voidptr, symbol string) voidptr {
-	return C.dlsym(handle, symbol.str)
+	return C.dlsym(handle, charptr(symbol.str))
 }