http: set the proxy SSL options, if compiling with a new-enough libcurl

As of v7.52.0, libcurl allows to specify not only the SSL options for
the actual HTTPS connection, but also for the HTTPS proxy (if any).

Let's do that.

This _may_ address git-for-windows#4467.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

git-curl-compat.h

@@ -100,6 +100,7 @@
  */
 #if LIBCURL_VERSION_NUM >= 0x073400
 #define GIT_CURL_HAVE_CURLOPT_PROXY_CAINFO 1
+#define GIT_CURL_HAVE_CURLOPT_PROXY_SSL_OPTIONS 1
 #endif
 
 /**

http.c

@@ -1028,8 +1028,12 @@ static CURL *get_curl_handle(void)
 #endif
 		}
 
-		if (ssl_options)
+		if (ssl_options) {
 			curl_easy_setopt(result, CURLOPT_SSL_OPTIONS, ssl_options);
+#ifdef GIT_CURL_HAVE_CURLOPT_PROXY_SSL_OPTIONS
+			curl_easy_setopt(result, CURLOPT_PROXY_SSL_OPTIONS, ssl_options);
+#endif
+		}
 	}
 
 	if (http_proactive_auth)