[compiler-rt][builtins] Add helper functions for uint16/sint16/uint8/sint8 div and mod

__udivmodhi4 : uint16 div and mod
__udivmodqi4 : uint8 div and mod
__divmodhi4  : sint16 div and mod
__divmodqi4  : sint8 div and mod

The above helper functions in libgcc have special ABI as described at
https://gcc.gnu.org/wiki/avr-gcc#Exceptions_to_the_Calling_Convention .

Reviewed By: aykevl

Differential Revision: https://reviews.llvm.org/D124600