PPC NCG: Implement callish prim ops

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).

Test Plan: validate on AIX and 32-bit Linux

Reviewers: simonmar, erikd, hvr, austin, bgamari

Reviewed By: erikd, hvr, bgamari

Subscribers: trofi, kgardas, thomie

Differential Revision: https://phabricator.haskell.org/D2973

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