Fix PrepareCallCFunction and CallCFunctionHelper ABI
Fix 64-bit kNumRequiredStackFrameSlots to 20
PERF: Exploit RISBG in ExtractBitRange and optimize CheckPageFlag
Minor improvements in various sequences
cleanup DirectCEntryStub
Fix CEntryStub and move RA address in EnterExitFrame
Replace basr by larl+bcr to work around top bit in return address
Cleanup PPC ABI
Fix floating point ABI -- save correct volatile fp regs to stack