Fix Issue 10915 - std.typecons.Nullable throws in writeln() if it's null
Add support of IeeFlags and FloatingPointControl for PPC32/64.

This corrects some existings 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 functionaly has been verified on a Linux/PPC64le system with LDC. The LDC
specific implementation is left out.
std.json: Fixed issue 12969. opIndexAssign operator for JSONValue added. Changed order of elements in enum JSON_TYPE so NULL is a default type when JSONValue is not initialized

Signed-off-by: Uranuz <neuranuz@gmail.com>
Deleted leading and trailing spaces inside *if* to match code style
Remove non `auto ref` opAssign overload

It conflicts with new one and should be completely covered by the nature
of auto ref.
Merge pull request #2611 from redstar/math

Add support of IEEE Flags and FloatingPointControl for PPC32/64.
Merge pull request #2587 from MetaLang/nullable-tostring

Fix Issue 10915 - std.typecons.Nullable throws in writeln() if it's null
Merge pull request #2607 from Dicebot/uranuz_issue_12969

Fix issue 12969 : opIndexAssign operator for JSONValue