uemacs: input.c: Fix mkstemp warning.

Fix the following warning:

input.c: In function ‘getstring’:
input.c:590: warning: ignoring return value of ‘mkstemp’, declared with attribute warn_unused_result

This add usage.c module for die function.
This also add wrapper.c module for the xmkstemp that is wrapper function
around the original mkstemp function.

Both module codes was largelly based on git, linux and sparse codes.

Signed-off-by: Thiago Farina <tfransosi@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

usage.c

@@ -0,0 +1,22 @@
+#include "usage.h"
+
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static void report(const char* prefix, const char *err, va_list params)
+{
+	char msg[4096];
+	vsnprintf(msg, sizeof(msg), err, params);
+	fprintf(stderr, "%s%s\n", prefix, msg);
+}
+
+void die(const char* err, ...)
+{
+	va_list params;
+
+	va_start(params, err);
+	report("fatal: ", err, params);
+	va_end(params);
+	exit(128);
+}