[endian] update the endian.h file to use builtins and tighten up a macro
[endian] update the endian.h file to use builtins and tighten up a macro

Use compiler builtins for these and make the *E32SWAP routines a bit safer.

hollanderic/lkstuff,littlekernel/lk,hollanderic/lkstuff,littlekernel/lk,littlekernel/lk,littlekernel/lk,hollanderic/lkstuff,hollanderic/lkstuff