stupidgcm: fix build with CGO_ENABLED=1 without_openssl

We missed some "// +build" lines

internal/stupidgcm/Makefile

@@ -1,3 +1,14 @@
+.PHONY: test
+test: gcc
+	# All three ways of building this must work
+	go build
+	go build -tags without_openssl
+	CGO_ENABLED=0 go build -tags without_openssl
+	# Likewise, all three ways of testing this must work
+	go test -v
+	go test -v -tags without_openssl
+	CGO_ENABLED=0 go test -v -tags without_openssl
+
 .PHONY: gcc
 gcc:
 	gcc -Wall -Wextra -Wformat-security -Wconversion -lcrypto -c *.c

internal/stupidgcm/common.go

@@ -1,3 +1,5 @@
+// +build !without_openssl
+
 package stupidgcm
 
 import (

internal/stupidgcm/openssl_aead.c

@@ -1,3 +1,5 @@
+// +build !without_openssl
+
 #include "openssl_aead.h"
 #include <openssl/evp.h>
 #include <stdio.h>