Fix issue I introduced reworking platform-specific code

I verified things compile now like this

CGO_ENABLED=0 GOOS=windows go install -gcflags="all=-N -l" ./...
CGO_ENABLED=0 GOOS=darwin GOARCH=amd64 go install -gcflags="all=-N -l" ./...
CGO_ENABLED=0 GOOS=darwin GOARCH=arm64 go install -gcflags="all=-N -l" ./...
CGO_ENABLED=0 GOOS=freebsd GOARCH=amd64 go install -gcflags="all=-N -l" ./...
CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go install -gcflags="all=-N -l" ./...
CGO_ENABLED=0 GOOS=linux GOARCH=arm go install -gcflags="all=-N -l" ./...
CGO_ENABLED=0 GOOS=linux GOARCH=arm64 go install -gcflags="all=-N -l" ./...
CGO_ENABLED=0 GOOS=netbsd GOARCH=amd64 go install -gcflags="all=-N -l" ./...
CGO_ENABLED=0 GOOS=openbsd GOARCH=amd64 go install -gcflags="all=-N -l" ./...
CGO_ENABLED=0 GOOS=linux GOARCH=riscv64 go install -gcflags="all=-N -l" ./...

system/dumpcapext_arm64.go

@@ -2,6 +2,9 @@
 // code is governed by the MIT license that can be found in the LICENSE
 // file.
 
+// +build !darwin
+// +build !linux
+
 package system
 
 import (