schannel: use Curl_ prefix for global private symbols

Curl_verify_certificate() must use the Curl_ prefix since it is globally
available in the lib and otherwise steps outside of our namespace!

Closes #3201

lib/vtls/schannel.c

@@ -1114,7 +1114,7 @@ schannel_connect_step2(struct connectdata *conn, int sockindex)
 
 #ifdef HAS_MANUAL_VERIFY_API
   if(conn->ssl_config.verifypeer && BACKEND->use_manual_cred_validation) {
-    return verify_certificate(conn, sockindex);
+    return Curl_verify_certificate(conn, sockindex);
   }
 #endif
 

lib/vtls/schannel.h

@@ -8,7 +8,7 @@
  *                             \___|\___/|_| \_\_____|
  *
  * Copyright (C) 2012, Marc Hoersken, <info@marc-hoersken.de>, et al.
- * Copyright (C) 2012 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 2012 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -53,7 +53,7 @@
 
 extern const struct Curl_ssl Curl_ssl_schannel;
 
-CURLcode verify_certificate(struct connectdata *conn, int sockindex);
+CURLcode Curl_verify_certificate(struct connectdata *conn, int sockindex);
 
 /* structs to expose only in schannel.c and schannel_verify.c */
 #ifdef EXPOSE_SCHANNEL_INTERNAL_STRUCTS

lib/vtls/schannel_verify.c

@@ -406,7 +406,7 @@ cleanup:
   return result;
 }
 
-CURLcode verify_certificate(struct connectdata *conn, int sockindex)
+CURLcode Curl_verify_certificate(struct connectdata *conn, int sockindex)
 {
   SECURITY_STATUS status;
   struct Curl_easy *data = conn->data;