Tidy RegStorage for X86.

Don't use global variables initialized in constructors to hold onto constant
values, instead use the TargetReg32 helper. Improve this helper with the use
of lookup tables. Elsewhere prefer to use constexpr values as they will have
less runtime cost.
Add an ostream operator to RegStorage for CHECK_EQ and use.

Change-Id: Ib8d092d46c10dac5909ecdff3cc1e18b7e9b1633
14 files changed