xkbcomp: Use fread() instead of getc()

xkbcomp: Use fread() instead of getc()

So, it turns out that if you're parsing a fairly large amount of data,
using getc() to get all the input rather than, say, read(), is some kind
of remarkably daft and unperformant idea.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>