x86_64: Fix intrinsics

The following intrinsics have been ported:

- Abs(double/long/int/float)
- String.indexOf/charAt/compareTo/is_empty/length
- Float.floatToRawIntBits, Float.intBitsToFloat
- Double.doubleToRawLongBits, Double.longBitsToDouble
- Thread.currentThread
- Unsafe.getInt/Long/Object, Unsafe.putInt/Long/Object
- Math.sqrt, Math.max, Math.min
- Long.reverseBytes

Math.min and max for longs have been implemented for x86_64.

Commented out until good tests available:
- Memory.peekShort/Int/Long, Memory.pokeShort/Int/Long

Turned off on x86-64 as reported having problems
- Cas

Change-Id: I934bc9c90fdf953be0d3836a17b6ee4e7c98f244