libcrypto-compat: fix HMAC_CTX_free for OpenSSL < 1.1.0

On older OpenSSL versions, the EVP_MD_CTX fields within an HMAC_CTX
structure are contained inlined (change here [1]): be sure to not
try to free those fields on those builds.

Found running the `pkd_hello` test with:

    valgrind ./pkd_hello -i1 -t torture_pkd_openssh_dsa_rsa_default

^ valgrind will cite "Invalid free() ..." errors which are present
before this fix and absent after, when building with OpenSSL 1.0.1.

[1] 6e59a892db

Signed-off-by: Jon Simons <jon@jonsimons.org>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

src/libcrypto-compat.c

@@ -304,9 +304,11 @@ void HMAC_CTX_free(HMAC_CTX *ctx)
 {
     if (ctx != NULL) {
         hmac_ctx_cleanup(ctx);
+#if OPENSSL_VERSION_NUMBER > 0x10100000L
         EVP_MD_CTX_free(&ctx->i_ctx);
         EVP_MD_CTX_free(&ctx->o_ctx);
         EVP_MD_CTX_free(&ctx->md_ctx);
+#endif
         OPENSSL_free(ctx);
     }
 }