Fix conditional check for HAVE_DECL_SECUREZEROMEMORY
Fix conditional check for HAVE_DECL_SECUREZEROMEMORY

"Unlike the other `AC_CHECK_*S' macros, when a symbol is not declared,
HAVE_DECL_symbol is defined to `0' instead of leaving HAVE_DECL_symbol
undeclared. When you are sure that the check was performed,
use HAVE_DECL_symbol in #if."

Source: autoconf documentation for AC_CHECK_DECLS.

libssh2/libssh2,libssh2/libssh2,libssh2/libssh2,libssh2/libssh2