Fix build on OS X 10.6

The assembler on older Mac's is buggy and requires 'movd' instructions
instead of 'movq' on x64. This is worked around in newer GCCs, but for
older ones it is easier to just not build LLint.

Do not use automatic conversion of Function<> to BLOCK.

Change-Id: I623c91acc79cd3476c441e1c981a2152de05d00c
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@digia.com>