libssh: Support building for native and nativesdk

Since libssh is now a dependency of cryptsetup, it needs to be buildable
for the same cases as cryptsetup.

Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-oe/recipes-support/libssh/libssh_0.8.9.bb

@@ -33,3 +33,5 @@ do_configure:prepend () {
 }
 
 TOOLCHAIN = "gcc"
+
+BBCLASSEXTEND = "native nativesdk"