s390-tools: Add function util_strstrip

Function strstrip strips leading and trailung
spaces from a given string.
During review it was decided to move this function
to the libutil library to make it available for other tools.

Signed-off-by: Thomas Richter <tmricht@linux.vnet.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

include/lib/util_str.h

@@ -0,0 +1,25 @@
+/**
+ * @defgroup util_str
+ * @{
+ * @brief Strip leading and trailing blanks
+ *
+ * Copyright IBM Corp. 2018
+ *
+ * s390-tools is free software; you can redistribute it and/or modify
+ * it under the terms of the MIT license. See LICENSE for details.
+ */
+
+#ifndef LIB_UTIL_STR_H
+#define LIB_UTIL_STR_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+char *util_strstrip(char *s);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /** LIB_UTIL_STRSTRIP_H @} */