HPCC-9608 Potentially unsafe code in 64-bit constant-folding

We hit the issue in 32-bit, where code between two asm sections failed because
assumed sp was correct between them. While we have not observed the issue in
x64 (and maybe never would) I think this code is safer.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #6275 from richardkchapman/fold64bit

HPCC-9608 Potentially unsafe code in 64-bit constant-folding

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>