Provide PowerPC optimised implementations of callish prim ops.

MO_?_QuotRem

The generic implementation of quotient remainder prim ops uses

a division and a remainder operation. There is no remainder on

PowerPC and so we need to implement remainder "by hand" which

results in a duplication of the divide operation when using the

generic code.

Avoid this duplication by implementing the prim op in the native

code generator.

MO_U_Mul2

Use PowerPC's instructions for long multiplication.

Addition and subtraction

Use PowerPC add/subtract with carry/overflow instructions

MO_Clz and MO_Ctz

Use PowerPC's CNTLZ instruction and implement count trailing

zeros using count leading zeros

MO_QuotRem2

Implement an algorithm given by Henry Warren in "Hacker's Delight"

using PowerPC divide instruction. TODO: Use long division instructions

when available (POWER7 and later).