metrics: disable CPU stats (gosigar) on Darwing when nocgo is passed

[BogdanHabic]

As the title suggests disables gosigar on darwin when CGO is disabled.

This is because the build fails with the following error when CGO is disabled:

../../../../pkg/mod/github.com/elastic/gosigar@v0.10.5/concrete_sigar.go:20:11: cpuUsage.Get undefined (type Cpu has no field or method Get)
../../../../pkg/mod/github.com/elastic/gosigar@v0.10.5/concrete_sigar.go:30:13: cpuUsage.Get undefined (type Cpu has no field or method Get)
../../../../pkg/mod/github.com/elastic/gosigar@v0.10.5/concrete_sigar.go:49:10: l.Get undefined (type LoadAverage has no field or method Get)
../../../../pkg/mod/github.com/elastic/gosigar@v0.10.5/concrete_sigar.go:55:10: m.Get undefined (type Mem has no field or method Get)
../../../../pkg/mod/github.com/elastic/gosigar@v0.10.5/concrete_sigar.go:61:10: s.Get undefined (type Swap has no field or method Get)
../../../../pkg/mod/github.com/elastic/gosigar@v0.10.5/concrete_sigar.go:67:10: p.Get undefined (type HugeTLBPages has no field or method Get)
../../../../pkg/mod/github.com/elastic/gosigar@v0.10.5/concrete_sigar.go:79:11: fd.Get undefined (type FDUsage has no field or method Get)
../../../../pkg/mod/github.com/elastic/gosigar@v0.10.5/sigar_darwin_amd64.go:11:12: undefined: sysctlbyname

[karalabe]

This looks very weird. Architectures mixed with platforms. It would also be a maintenance nightmare to keep it always updated. Please use exclusion patterns

[karalabe]

Ping @BogdanHabic

[adamschmideg]

@BogdanHabic are you still interested in this PR and in making the changes requested?

[BogdanHabic]

@adamschmideg oh my god, sorry, yes, I somehow missed this notification due to the security ones GitHub has spammed me with. I'll make the changes today!

[BogdanHabic]

Hey @adamschmideg, I've pushed the requested change. The test that is failing is not broken by this change if I'm not mistaken.

[karalabe]

I think you should be able to cover all cases here and not need that extra file:

// +build !ios
// +build !darwin cgo

Could you try this version out?

[adamschmideg]

I think it should be

Suggested change

	// +build !ios,!darwin
	// +build !ios,!darwin darwin,cgo

[adamschmideg]

This is the truth table I'm using

ios	darwin	Other OS	cgo	cpu enabled
0	1	0	0	0
0	1	0	1	1
1	0	0	0	0
1	0	0	1	0
0	0	1	0	1
0	0	1	1	1

[BogdanHabic]

So the Other OS will essentially be caught by !ios,!darwin, correct? If this is the case, the change you suggested makes sense.

[renaynay]

Closing this PR as this fix was not sufficient to prevent geth build failure when building on darwin with CGO disabled. #21041 implements a fix for this issue.