Better support for cross-compiling.

Better support for cross-compiling.

It is difficult to cross compile pciutils, as the host is not standard 3 or 4 components and one need to pass all tools cross compile prefixes.

The attached patch makes it easier:

1. Add CROSS_COMPILE prefix for all toolchain tools. I also changed default CC
   to gcc, I can fix this if you like.

2. Allow parsing standard HOST, such as i686-pc-linux-gnu.

3. Make rel be RELEASE, maybe the whole release thing can be removed as it is
   not actually used.

Signed-off-by: Alon Bar-Lev <alon.barlev@gmail.com>