In order to protect users of prebid-server that don't use CGO, add build flag

modules/builder.go

@@ -1,19 +1,17 @@
 package modules
 
 import (
-	fiftyonedegreesDevicedetection "github.com/prebid/prebid-server/v3/modules/fiftyonedegrees/devicedetection"
 	prebidOrtb2blocking "github.com/prebid/prebid-server/v3/modules/prebid/ortb2blocking"
 )
 
 // builders returns mapping between module name and its builder
 // vendor and module names are chosen based on the module directory name
 func builders() ModuleBuilders {
-	return ModuleBuilders{
-		"fiftyonedegrees": {
-			"devicedetection": fiftyonedegreesDevicedetection.Builder,
-		},
+	ret := ModuleBuilders{
 		"prebid": {
 			"ortb2blocking": prebidOrtb2blocking.Builder,
 		},
 	}
+	addFiftyonedegreesDevicedetection(ret)
+	return ret
 }

modules/cgo.go

@@ -0,0 +1,14 @@
+//go:build cgo
+
+package modules
+
+import (
+	fiftyonedegreesDevicedetection "github.com/prebid/prebid-server/v3/modules/fiftyonedegrees/devicedetection"
+)
+
+func addFiftyonedegreesDevicedetection(b ModuleBuilders) {
+	if b["fiftyonedegrees"] == nil {
+		b["fiftyonedegrees"] = make(map[string]ModuleBuilderFn)
+	}
+	b["fiftyonedegrees"]["devicedetection"] = fiftyonedegreesDevicedetection.Builder
+}

modules/no-cgo.go

@@ -0,0 +1,7 @@
+//go:build !cgo
+
+package modules
+
+func addFiftyonedegreesDevicedetection(b ModuleBuilders) {
+	// Do nothing - fiftyonedegrees module is not supported without cgo
+}