Fix -Werror=discarded-qualifiers warning in openssl

* Upstream fix: ruby/openssl@6fb3499a7b
* On gcc only:
compiling ossl_pkey_ec.c
ossl_pkey_ec.c: In function ‘ossl_ec_key_check_key’:
ossl_pkey_ec.c:24:11: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
   24 |     (key) = EVP_PKEY_get0_EC_KEY(_pkey); \
      |           ^
ossl_pkey_ec.c:489:5: note: in expansion of macro ‘GetEC’
  489 |     GetEC(self, ec);
      |     ^~~~~

Author: eregon

lib/truffle/rbconfig.rb

@@ -108,8 +108,6 @@ module RbConfig
     '-Wno-format-extra-args',          # Our PRIsVALUE generates this because compilers ignore printf extensions
   ]
   warnflags << '-Wno-format-invalid-specifier' if clang # Our PRIsVALUE generates this because compilers ignore printf extensions
-  # TODO fix it, happens in openssl
-  warnflags << '-Wno-discarded-qualifiers' if gcc
 
   defs = ''
   cppflags = ''

src/main/c/openssl/ossl_pkey_ec.c

@@ -483,7 +483,7 @@ static VALUE ossl_ec_key_check_key(VALUE self)
 #ifdef HAVE_EVP_PKEY_CHECK
     EVP_PKEY *pkey;
     EVP_PKEY_CTX *pctx;
-    EC_KEY *ec;
+    const EC_KEY *ec;
 
     GetPKey(self, pkey);
     GetEC(self, ec);