Log Message:
g95: Fix netbsd/mips64 builds

NetBSD switched to n32 ABI for mips64el in NetBSD 6, and the build is
failing due to the default ABI mismatch between linker and newly built
compiler.

Default to n32 and backport n32 size definitions from newer GCC.

Small chance of a functional change for o32 builds (which should work), ride
previous PKGREVISION bump for it.