tsan: unify all shadow mappings

Currently we have ifdef's for Go/C++ and Windows/non-Windows
in MemToShadow, MemToMeta, ShadowToMem. This does not allow
to test all mappings on a single platform.
Make all these functions support a superset of mappings for
all platforms by defining missing mapping consts to 0.
E.g. we always do ^A+B, but if A and B are defined to 0,
then these operations become no-op.

Depends on D107739.

Reviewed By: melver

Differential Revision: https://reviews.llvm.org/D107740