[SeaBIOS] Deprecating gcc older than v4.6

[Kevin O'Connor]

Hi,

During the final v1.11.0 release tests I found that both gcc v3.4 and
gcc v4.4 (at least as shipped with Fedora 13) will no longer
successfully compile SeaBIOS.  The two different gcc versions failed
on two different errors.

Instead of trying to keep the code compatible with these old compilers
I went forward with the release as is.  I don't think there is a
compelling reason to continue to support these old versions of gcc.

The gcc v4.6.0 (at least as shipped on Fedora 15) continues to build
SeaBIOS successfully.

-Kevin