Move PPC's getDataLayoutString out of line and document it better.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196987 91177308-0d34-0410-b5e6-96231b3b80d8
One ppc32-darwin, a i64 inside a structure can have 32 bit alignment.

Thanks for Iain Sandoe for testing this with the original gcc.

Clang was already getting this right.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197572 91177308-0d34-0410-b5e6-96231b3b80d8

Conflicts:
	lib/Target/PowerPC/PPCTargetMachine.cpp
Fix f64 and f128 for ppc-darwin.

This patch adds -f64:32:64 to 32 bit ppc darwin since a f64 inside a
structure are only 32 bit aligned.

The patch also drop -f128:64:128 from all ppc darwin, since f128 is
128 bit aligned.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197574 91177308-0d34-0410-b5e6-96231b3b80d8

Conflicts:
	lib/Target/PowerPC/PPCTargetMachine.cpp