Fixed undeclared 'uuid_data' build error

Fixed the following build error on Linux (Fedora 20 3.14.9-200.fc20.x86_64) using libuuid 2.24.2 from util-linux:
```
Scanning dependencies of target crossuuid
[ 33%] Building C object CMakeFiles/crossuuid.dir/crossuuid.c.o
/home/travis/Desktop/crossuuid/crossuuid.c: In function ‘_generate_uuid_bytes’:
/home/travis/Desktop/crossuuid/crossuuid.c:211:26: error: ‘uuid_data’ undeclared (first use in this function)
  memcpy(data, id, sizeof(uuid_data));
                          ^
/home/travis/Desktop/crossuuid/crossuuid.c:211:26: note: each undeclared identifier is reported only once for each function it appears in
make[2]: *** [CMakeFiles/crossuuid.dir/crossuuid.c.o] Error 1
make[1]: *** [CMakeFiles/crossuuid.dir/all] Error 2
make: *** [all] Error 2

```