fix build on win32
Use the most portable POSIX-style non-blocking I/O (O_NONBLOCK) instead of BSD-style through FIONBIO. It turns out Tru64 and probably IRIX don't support the latter when fd is a pipe (slirp case).
Fixes for IRIX/mips build with MIPSPro compilers
minor cleanups
slirp user mode network emulation code from qemu
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