native x86_64 support

Here are some patches that make it run natively on x86_64 linux.

The regression test resuls with rebol-test shows four more successes than 32-bit.

Native x86_64 version:

```
system/version: 2.101.0.4.40
code-checksum: #{C60C3F4249FAA08A4B268BB2979838F12E67083D}
test-checksum: #{8750ABB0F94507CF9ABB4B2376415C7EB576454D}
Total: 4657
Succeeded: 4176
Test-failures: 156
Crashes: 17
Dialect-failures: 0
Skipped: 308
```

32-bit binary on x86_64 system:

```
system/version: 2.101.0.4.4
code-checksum: #{3AE16D64BB531AF17447CEE3E3AFC24356BB5A3F}
test-checksum: #{8750ABB0F94507CF9ABB4B2376415C7EB576454D}
Total: 4657
Succeeded: 4172
Test-failures: 156
Crashes: 21
Dialect-failures: 0
Skipped: 308
```