Optimize generic 64-bit division code

FPC_{DIV,MOD}_QWORD now check if both inputs have their upper 32bit set
to zero and in that case use 32-bit division instead, which many
plattforms can either do in hardware or have optimized assembly code
for.

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@28279 3ad0048d-3df7-0310-abae-a5850022a9f2