metrics: add go:build lines (ethereum#23468)

metrics/cpu_disabled.go

@@ -14,6 +14,7 @@
 // You should have received a copy of the GNU Lesser General Public License
 // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
 
+//go:build ios || js
 // +build ios js
 
 package metrics

metrics/cputime_nop.go

@@ -14,6 +14,7 @@
 // You should have received a copy of the GNU Lesser General Public License
 // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
 
+//go:build windows || js
 // +build windows js
 
 package metrics

metrics/runtime_cgo.go

@@ -1,3 +1,4 @@
+//go:build cgo && !appengine && !js
 // +build cgo,!appengine,!js
 
 package metrics

metrics/runtime_gccpufraction.go

@@ -1,3 +1,4 @@
+//go:build go1.5
 // +build go1.5
 
 package metrics

metrics/runtime_no_cgo.go

@@ -1,3 +1,4 @@
+//go:build !cgo || appengine || js
 // +build !cgo appengine js
 
 package metrics

metrics/runtime_no_gccpufraction.go

@@ -1,3 +1,4 @@
+//go:build !go1.5
 // +build !go1.5
 
 package metrics

metrics/syslog.go

@@ -1,3 +1,4 @@
+//go:build !windows
 // +build !windows
 
 package metrics