Enhance printing OpenSSL versions.

* Updated the `OpenSSL::OPENSSL_VERSION_NUMBER` comment explaining the format.
* Added the `OpenSSL::LIBRESSL_VERSION_NUMBER` to print LibreSSL version number.
  The value is `nil` in the OpenSSL case. Note
  `test/openssl/utils.rb#libressl?` is not using this value in it.
* Update `rake debug` to print the values in a readable way, adding
  `OpenSSL::OPENSSL_VERSION_NUMBER` and `OpenSSL::LIBRESSL_VERSION_NUMBER`.

Rakefile

@@ -38,7 +38,17 @@ task :debug_compiler do
 end
 
 task :debug do
-  ruby "-I./lib -ropenssl -ve'puts OpenSSL::OPENSSL_VERSION, OpenSSL::OPENSSL_LIBRARY_VERSION'"
+  ruby_code = <<~'EOF'
+  libre_version_number_str = (!OpenSSL::LIBRESSL_VERSION_NUMBER.nil?) ?
+    OpenSSL::LIBRESSL_VERSION_NUMBER.to_s(16) : "nil"
+  puts <<~'MESSAGE'
+  OpenSSL::OPENSSL_VERSION: #{OpenSSL::OPENSSL_VERSION}
+  OpenSSL::OPENSSL_LIBRARY_VERSION: #{OpenSSL::OPENSSL_LIBRARY_VERSION}
+  OpenSSL::OPENSSL_VERSION_NUMBER: #{OpenSSL::OPENSSL_VERSION_NUMBER.to_s(16)}
+  OpenSSL::LIBRESSL_VERSION_NUMBER: #{libre_version_number_str}
+  MESSAGE
+  EOF
+  ruby %Q(-I./lib -ropenssl -ve'#{ruby_code}')
 end
 
 task :default => :test

ext/openssl/ossl.c

@@ -1150,9 +1150,29 @@ Init_openssl(void)
     /*
      * Version number of OpenSSL the ruby OpenSSL extension was built with
      * (base 16)
+     *
+     * OpenSSL 3: 0xMNN00PP0 (major minor 00 patch 0)
+     * OpenSSL 1: 0xMNNFFPPS (major minor fix patch status)
+     * LibreSSL : 0x20000000 (fixed value)
+     *
+     * See also the man page OPENSSL_VERSION_NUMBER(3).
      */
     rb_define_const(mOSSL, "OPENSSL_VERSION_NUMBER", INT2NUM(OPENSSL_VERSION_NUMBER));
 
+    /*
+     * Version number of LibreSSL the ruby OpenSSL extension was built with
+     * (base 16)
+     *
+     * LibreSSL: 0xMNNFFPPS (major minor fix patch status)
+     *
+     * See also the man page OPENSSL_VERSION_NUMBER(3).
+     */
+#if defined(LIBRESSL_VERSION_NUMBER)
+    rb_define_const(mOSSL, "LIBRESSL_VERSION_NUMBER", INT2NUM(LIBRESSL_VERSION_NUMBER));
+#else
+    rb_define_const(mOSSL, "LIBRESSL_VERSION_NUMBER", Qnil);
+#endif
+
     /*
      * Boolean indicating whether OpenSSL is FIPS-capable or not
      */