crypto: fix build directives

crypto/secp256k1/panic_cb.go

@@ -2,7 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be found in
 // the LICENSE file.
 
-// +build !gofuzz cgo
+// +build !gofuzz
+// +build cgo
 
 package secp256k1
 

crypto/secp256k1/scalar_mult_cgo.go

@@ -2,7 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be found in
 // the LICENSE file.
 
-// +build !gofuzz cgo
+// +build !gofuzz
+// +build cgo
 
 package secp256k1
 

crypto/secp256k1/secp256.go

@@ -2,7 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be found in
 // the LICENSE file.
 
-// +build !gofuzz cgo
+// +build !gofuzz
+// +build cgo
 
 // Package secp256k1 wraps the bitcoin secp256k1 C library.
 package secp256k1