libssh: improve the deprecation warning dismissal

Previous code was compiler dependant, and dismissed all deprecation warnings
indiscriminately.

libssh provides a way to disable the deprecation warnings for libssh only, and
naturally this is the preferred way.

This commit uses that, to prevent the erroneous hiding of potential, unrelated
deprecation warnings.

Fixes #12519
Closes #12520

lib/vssh/libssh.c

@@ -31,6 +31,11 @@
 
 #include <limits.h>
 
+/* in 0.10.0 or later, ignore deprecated warnings */
+#include <libssh/libssh_version.h>
+#if (LIBSSH_VERSION_MINOR >= 10) || (LIBSSH_VERSION_MAJOR > 0)
+#define SSH_SUPPRESS_DEPRECATED
+#endif
 #include <libssh/libssh.h>
 #include <libssh/sftp.h>
 
@@ -89,14 +94,6 @@
 #include "curl_memory.h"
 #include "memdebug.h"
 
-/* in 0.10.0 or later, ignore deprecated warnings */
-#if defined(__GNUC__) &&                        \
-  (LIBSSH_VERSION_MINOR >= 10) ||               \
-  (LIBSSH_VERSION_MAJOR > 0)
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
-#endif
-
 /* A recent macro provided by libssh. Or make our own. */
 #ifndef SSH_STRING_FREE_CHAR
 #define SSH_STRING_FREE_CHAR(x)                 \
@@ -2957,10 +2954,4 @@ void Curl_ssh_version(char *buffer, size_t buflen)
   (void)msnprintf(buffer, buflen, "libssh/%s", ssh_version(0));
 }
 
-#if defined(__GNUC__) &&                        \
-  (LIBSSH_VERSION_MINOR >= 10) ||               \
-  (LIBSSH_VERSION_MAJOR > 0)
-#pragma GCC diagnostic pop
-#endif
-
 #endif                          /* USE_LIBSSH */