refactor error message-related functions

split message print fuctions (mpr_*), strerrno, and mscp_get/set_error
into print.c/h and strerrno.c/h.

ToDo: revise usages of priv_set_errv and pr_* functions.

src/strerrno.c

@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-3.0-only */
+
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdarg.h>
+
+#include <strerrno.h>
+
+#define STRERRNO_TLS_BUFSIZ	128
+__thread char tls_strerrno_buf[STRERRNO_TLS_BUFSIZ];
+
+const char *strerrno(void)
+{
+	snprintf(tls_strerrno_buf, sizeof(tls_strerrno_buf), "%s", "strerror_r error");
+	strerror_r(errno, tls_strerrno_buf, sizeof(tls_strerrno_buf));
+	return tls_strerrno_buf;
+}
+
+#define PRIV_ERR_BUFSIZ	(1 << 12)
+static char priv_err_buf[PRIV_ERR_BUFSIZ], internal[PRIV_ERR_BUFSIZ];
+
+void priv_set_err(const char *fmt, ...)
+{
+	va_list va;
+
+	/* arguments may contains priv_err_buf. Thus, we build the
+	 * string in a internal buffer, and then copy it to
+	 * priv_err_buf. */
+        memset(internal, 0, sizeof(internal));
+        va_start(va, fmt);
+        vsnprintf(internal, sizeof(internal), fmt, va);
+        va_end(va);	
+
+	snprintf(priv_err_buf, sizeof(priv_err_buf), "%s", internal);
+}
+
+const char *priv_get_err()
+{
+	return priv_err_buf;
+}