Use "GO386=softfloat" to compile Go for Pentium

Cross-compiling is trivial with pure-Go projects. For example, to compile for a Pentium (maybe even a 486 DX?) running NetBSD, just set a few variables:

GOOS=netbsd GOARCH=386 GO386=softfloat make

The GO386=softfloat setting is necessary for Pentium I/II--without specifying it, Go 1.16 requires SSE2 by default for "GOARCH=386", and I believe that's only supported on Pentium 4+.

Why do I know this? I have a late '90s Dell Latitude CP (Pentium 233 MHz with 128 MB RAM) running NetBSD and I wanted to run the aerc mail client on it. Unfortunately, the prebuilt "i386" NetBSD package crashed with SIGILL (illegal instruction). Loading the core dump into GDB revealed that an xorps instruction was the problem because that instruction was introduced as part of SSE2 (well after my Pentium was manufactured). I have not yet investigated whether or not it's expected for prebuilt binary packages on "i386" NetBSD to require a Pentium 4, but in my case recompiling the pure-Go aerc project was trivial and I can now read modern email on a nearly 30 year old computer.