Fixed build on ARM systems without configure scripts.

Numerous projects have cropped up with compile issues traced to this file.
An example test case:

include <stdio.h>
include "include/curl/curlbuild.h.dist"
int main() {	printf("%s\n", CURL_FORMAT_CURL_OFF_T);}

This file will fail to compile on a Raspberry pi due to running GCC,
on neither i386, ppc or x64.
Whilst the correctly using the ./configure script resolves this issue, multiple products without configure scripts have simply included this file.