fix: recognize backslash separators in fpack basename/relpath (Windows only)

tools/fpack.c

@@ -59,17 +59,23 @@ static char *join_path(const char *dir, const char *name)
 	return out;
 }
 
+#ifdef _WIN32
+#define IS_PATH_SEP(c) ((c) == '/' || (c) == '\\')
+#else
+#define IS_PATH_SEP(c) ((c) == '/')
+#endif
+
 static char *basename_dup(const char *path)
 {
 	size_t end = strlen(path);
 	size_t start;
 	char *out;
 
-	while (end > 0 && path[end - 1] == '/')
+	while (end > 0 && IS_PATH_SEP(path[end - 1]))
 		end--;
 
 	start = end;
-	while (start > 0 && path[start - 1] != '/')
+	while (start > 0 && !IS_PATH_SEP(path[start - 1]))
 		start--;
 
 	out = malloc(end - start + 1);
@@ -262,7 +268,7 @@ int main(int argc, char **argv)
 	output = output_arg ? dup_str(output_arg) : derive_output_name(input_dir);
 
 	base_len = strlen(input_dir);
-	while (base_len > 0 && input_dir[base_len - 1] == '/')
+	while (base_len > 0 && IS_PATH_SEP(input_dir[base_len - 1]))
 		base_len--;
 
 	w = fpk_writer_open(output);