stand: gptboot: fix build with xtoolchain-llvm90

ufsread.c grows a dependency on __ashldi3 with llvm90. For gptboot, just
start pulling in ashldi3.c ashrdi3.c lshrdi3.c into libsa for all archs as
the number of archs requiring one or more of them keeps growing. qdivrem.c
and quad.h can be trivially kicked out of libsa if we start pulling these
from compiler-rt as qdivrem was only used to implement umoddi3, divdi3,
moddi3 (also in qdivrem.c).

Reviewed by: imp
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D21291