all: update build constraints to Go 1.17

Do it all at once in preparation for Go 1.18 support.

To make this commit, I've simply modified the `fmt-check` Makefile
target to rewrite files instead of listing the differences. So this is a
fully mechanical change, it should not have introduced any errors.

src/os/dir_test.go

@@ -1,3 +1,4 @@
+//go:build darwin || (linux && !baremetal && !js && !wasi && !386 && !arm)
 // +build darwin linux,!baremetal,!js,!wasi,!386,!arm
 
 package os_test