go-fuzz-build: build fails at tip Go due to missing abi_amd64.h (new in go1.17)

[thepudds]

$ go-fuzz-build -func=foo
[stderr]
failed to execute go build: exit status 2
# runtime
../.tmp/go-fuzz-build3057684113/goroot/src/runtime/asm_amd64.s:10: 
#include: open $WORK/.t mp/go-fuzz-build3057684113/goroot/pkg/include/cgo/abi_amd64.h: no such file or directory

Depending on what you are fuzzing, you might first hit #313, which is a separate tip failure.

I (hopefully!) have a PR for this...