Add -fclasses

microD will support classes, but this will be useful for -fstandalone: A
mode which will not require any external functions. (gcc.attributes and
gcc.builtins headers may still be required at compile time)
Revert "Fix Bug 139 - writes all-zero initialisers in the rodata section"

This reverts commit 0fcf8babc0d0af85a9a04aaa23b5856237fbdb9f.