The bitcoind make target in makefile.unix defines USE_UPNP to 0; however net.cpp among others uses '#ifdef' as the test for miniupnp, which means the upnp headers are always required.
I believe this is intentional. USE_UPNP=0 means that UPNP is not used by default but can be enabled. It's a three-way switch.
2) main.cpp has:
-char pchMessageStart[4] = { 0xf9, 0xbe, 0xb4, 0xd9 };
g++ 4.4.5 on DragonFly disapproves; the constants are being narrowed from int -> char inside an array initializer. I think the error is correct, though harsh.
Really? That's kind of a nutty error. Are you sure you aren't using non-standard warning flags? GCC will issue crazy warnings if you enable all possible warnings, even "unsigned char j[10], k[10]; j[ i ]^=k[ i ];" will trigger an int->char warning.