Fix AC_CHECK_DECLS usage in openssl.m4.
See:
https://www.gnu.org/software/autoconf/manual/autoconf-2.62/html_node/Generic-Declarations.html
"For each of the symbols (comma-separated list)"
When building with aggressive warning settings the current code results
in the following configure test code being generated:
#ifndef OpenSSL_add_all_algorithms EVP_aes_256_cfb
#ifdef __cplusplus
(void) OpenSSL_add_all_algorithms EVP_aes_256_cfb;
#else
(void) OpenSSL_add_all_algorithms EVP_aes_256_cfb;
#endif
#endif
Which is obviously wrong and makes the configure check fail.