accounts/keystore: enable fallback for darwin,!cgo (#19614)

Without this, accounts/keystore fails to build for Darwin with
CGO_ENABLED=0.

accounts/keystore/watch.go

@@ -14,7 +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/>.
 
-// +build darwin,!ios freebsd linux,!arm64 netbsd solaris
+// +build darwin,!ios,cgo freebsd linux,!arm64 netbsd solaris
 
 package keystore
 

accounts/keystore/watch_fallback.go

@@ -14,7 +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/>.
 
-// +build ios linux,arm64 windows !darwin,!freebsd,!linux,!netbsd,!solaris
+// +build darwin,!cgo ios linux,arm64 windows !darwin,!freebsd,!linux,!netbsd,!solaris
 
 // This is the fallback implementation of directory watching.
 // It is used on unsupported platforms.