version: add the CURL_VERSION_MULTI_SSL feature flag

This new feature flag reports When cURL was built with multiple SSL
backends.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

configure.ac

@@ -2420,14 +2420,25 @@ if test -z "$ssl_backends" -o "x$OPT_AXTLS" != xno; then
   test -z "$ssl_msg" || ssl_backends="${ssl_backends:+$ssl_backends, }$ssl_msg"
 fi
 
-if test "x$OPENSSL_ENABLED$GNUTLS_ENABLED$NSS_ENABLED$POLARSSL_ENABLED$MBEDTLS_ENABLED$AXTLS_ENABLED$CYASSL_ENABLED$WINSSL_ENABLED$DARWINSSL_ENABLED" = "x"; then
+case "x$OPENSSL_ENABLED$GNUTLS_ENABLED$NSS_ENABLED$POLARSSL_ENABLED$MBEDTLS_ENABLED$AXTLS_ENABLED$CYASSL_ENABLED$WINSSL_ENABLED$DARWINSSL_ENABLED" in
+x)
   AC_MSG_WARN([SSL disabled, you will not be able to use HTTPS, FTPS, NTLM and more.])
   AC_MSG_WARN([Use --with-ssl, --with-gnutls, --with-polarssl, --with-cyassl, --with-nss, --with-axtls, --with-winssl, or --with-darwinssl to address this.])
-else
-  # SSL is enabled, genericly
+  ;;
+x1)
+  # one SSL backend is enabled
   AC_SUBST(SSL_ENABLED)
   SSL_ENABLED="1"
-fi
+  ;;
+*)
+  # more than one SSL backend is enabled
+  AC_SUBST(SSL_ENABLED)
+  SSL_ENABLED="1"
+  AC_SUBST(CURL_WITH_MULTI_SSL)
+  CURL_WITH_MULTI_SSL="1"
+  AC_DEFINE(CURL_WITH_MULTI_SSL, 1, [built with multiple SSL backends])
+  ;;
+esac
 
 if test -n "$ssl_backends"; then
   curl_ssl_msg="enabled ($ssl_backends)"

docs/libcurl/curl_version_info.3

@@ -5,7 +5,7 @@
 .\" *                            | (__| |_| |  _ <| |___
 .\" *                             \___|\___/|_| \_\_____|
 .\" *
-.\" * Copyright (C) 1998 - 2015, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" * Copyright (C) 1998 - 2017, 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
@@ -156,6 +156,10 @@ libcurl ignore cookies with a domain that's on the list.
 .IP CURL_VERSION_HTTPS_PROXY
 libcurl was built with support for HTTPS-proxy.
 (Added in 7.52.0)
+.IP CURL_VERSION_MULTI_SSL
+libcurl was built with multiple SSL backends. For details, see
+\fIcurl_global_sslset(3)\fP.
+(Added in 7.56.0)
 .RE
 \fIssl_version\fP is an ASCII string for the OpenSSL version used. If libcurl
 has no SSL support, this is NULL.

docs/libcurl/symbols-in-versions

@@ -840,6 +840,7 @@ CURL_VERSION_KERBEROS4          7.10          7.33.0
 CURL_VERSION_KERBEROS5          7.40.0
 CURL_VERSION_LARGEFILE          7.11.1
 CURL_VERSION_LIBZ               7.10
+CURL_VERSION_MULTI_SSL          7.56.0
 CURL_VERSION_NTLM               7.10.6
 CURL_VERSION_NTLM_WB            7.22.0
 CURL_VERSION_PSL                7.47.0

include/curl/curl.h

@@ -2487,6 +2487,7 @@ typedef struct {
 #define CURL_VERSION_PSL          (1<<20) /* Mozilla's Public Suffix List, used
                                              for cookie domain verification */
 #define CURL_VERSION_HTTPS_PROXY  (1<<21) /* HTTPS-proxy support built-in */
+#define CURL_VERSION_MULTI_SSL    (1<<22) /* Multiple SSL backends available */
 
  /*
  * NAME curl_version_info()

lib/version.c

@@ -323,6 +323,9 @@ static curl_version_info_data version_info = {
 #endif
 #if defined(USE_LIBPSL)
   | CURL_VERSION_PSL
+#endif
+#if defined(CURL_WITH_MULTI_SSL)
+  | CURL_VERSION_MULTI_SSL
 #endif
   ,
   NULL, /* ssl_version */

packages/OS400/curl.inc.in

@@ -129,6 +129,8 @@
      d                 c                   X'00100000'
      d CURL_VERSION_HTTPS_PROXY...
      d                 c                   X'00200000'
+     d CURL_VERSION_MULTI_SSL...
+     d                 c                   X'00400000'
       *
      d CURL_HTTPPOST_FILENAME...
      d                 c                   X'00000001'

src/tool_help.c

@@ -503,7 +503,8 @@ static const struct feat feats[] = {
   {"TLS-SRP",        CURL_VERSION_TLSAUTH_SRP},
   {"HTTP2",          CURL_VERSION_HTTP2},
   {"UnixSockets",    CURL_VERSION_UNIX_SOCKETS},
-  {"HTTPS-proxy",    CURL_VERSION_HTTPS_PROXY}
+  {"HTTPS-proxy",    CURL_VERSION_HTTPS_PROXY},
+  {"MultiSSL",       CURL_VERSION_MULTI_SSL}
 };
 
 void tool_help(void)