Rewrite fputc in assembly

-36 bytes, -12% cycles

test/ref/test_fputc.c

@@ -0,0 +1,39 @@
+/*
+  !!DESCRIPTION!! fgets test
+  !!LICENCE!!     Public domain
+*/
+
+#include "common.h"
+
+#include <ctype.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+FILE *in, *out;
+int c, err;
+
+#define INFILE   "cf.in"
+
+int main(int argc,char **argv)
+{
+    in = fopen(INFILE, "rb");
+    if (in == NULL) {
+        return EXIT_FAILURE;
+    }
+
+    if (fputc(c, in) != EOF) {
+      printf("Error: can fputc to a file opened for reading\n");
+      return EXIT_FAILURE;
+    }
+    clearerr(in);
+
+    while ((c = fgetc(in)) != EOF) {
+      fputc(c, stdout);
+    }
+
+    fclose(in);
+    return 0;
+}