Support OpenSSL 3.0 Legacy provider in version 16

[herbrechtsmeier]

Node v16 supports dynamically linking with OpenSSL 3.0 (#29817) but doesn't support OpenSSL 3.0 Legacy provider (#40455). Please backport 86d1c0c or always load the legacy provider for OpenSSL 3.0.

[iamahuman]

If anyone is suffering from this issue on *nix, compiling the following code as a shared library and putting it into LD_PRELOAD environment variable may work as a stopgap measure:

#define _GNU_SOURCE
#include <stddef.h>
#include <stdint.h>
#include <dlfcn.h>
#include <openssl/ssl.h>
#include <openssl/provider.h>

int OPENSSL_init_ssl(uint64_t opts, const OPENSSL_INIT_SETTINGS *settings)
{
	static int once;
	static int (*orig_OPENSSL_init_ssl)(uint64_t opts, const OPENSSL_INIT_SETTINGS *settings);
	if (!__atomic_exchange_n(&once, 1, __ATOMIC_ACQ_REL))
	{
		*(void **)&orig_OPENSSL_init_ssl = dlsym(RTLD_NEXT, "OPENSSL_init_ssl");
		OSSL_PROVIDER_load(NULL, "legacy");
	}
	return (*orig_OPENSSL_init_ssl)(opts, settings);
}