kconfig: add xstrdup() helper

We already have xmalloc(), xcalloc(), and xrealloc(().  Add xstrdup()
as well to save tedious error handling.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/kconfig/util.c

@@ -154,3 +154,14 @@ void *xrealloc(void *p, size_t size)
 	fprintf(stderr, "Out of memory.\n");
 	exit(1);
 }
+
+char *xstrdup(const char *s)
+{
+	char *p;
+
+	p = strdup(s);
+	if (p)
+		return p;
+	fprintf(stderr, "Out of memory.\n");
+	exit(1);
+}