Previously we supplied only unsigned divisions on platforms that need software
division.
Yet compiler may itself use a signed division. A typical example would be a
difference between 2 pointers which involves division by object size.
The unaligned local in __aeabi_uidivmod leads to a store to a 64bit
value at an address that is not divisible by 8 (in grub_divmod64).
The compiler most likely generates a STRD instruction to store it and
this causes an exception.
Fixes Savannah bug #43632.
This includes improvements done by Leif Lindholm.
