Fix casting a pointer to an integer safely.

Fix casting a pointer to an integer safely.

Only casting from an integer (any size) to a pointer using reinterpret_cast<>
is well-defined. Casting a pointer to an integer needs a large enough integer.

Bug 29894961

Change-Id: I51cf6923f4feeaf1860ca0565aa7d40b61918e67
Reviewed-on: https://swiftshader-review.googlesource.com/5750
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>