Add support of IeeFlags and FloatingPointControl for PPC32/64.

This corrects some existing constants and adds new constants and logic.
Reading the PowerPC documentation is sometimes confusing because not only the CPU is big endian but also the bit numbering inside a word is reversed (old IBM style big endian).
The functionality has been verified on a Linux/PPC64le system with LDC. The LDC specific implementation is left out.