Fix environ Win32 build problem

src/builtin.c

@@ -1013,7 +1013,7 @@ static jv f_error(jq_state *jq, jv input, jv msg) {
 
 // FIXME Should autoconf check for this!
 #ifndef WIN32
-extern const char **environ;
+extern char **environ;
 #endif
 
 static jv f_env(jq_state *jq, jv input) {

src/compile.c

@@ -998,8 +998,8 @@ static int count_cfunctions(block b) {
   return n;
 }
 
-#ifdef WIN32
-extern const char **environ;
+#ifndef WIN32
+extern char **environ;
 #endif
 
 static jv