[scudo] Make Options a reference for functions.

Modify all places that use the Options structure to be a const
reference. The underlying structure is a u32 so making it a
reference doesn't really do anything. However, if the structure
changes in the future it already works and avoids future coders
wondering why a structure is being passed by value. This also
makes it clear that the Options should not be modified in those functions.

Reviewed By: Chia-hungDuan

Differential Revision: https://reviews.llvm.org/D156372