Add runtime markers for a full-width 32x32 multiply (0x12345678 * 0x9abcdef0
= 0x242d2080) and for a wide-dividend remainder, so a 16-bit-truncated MPYS or
a wrong FS1 cannot still produce the expected small results. Compute the 16x16
unsigned product in unsigned arithmetic to remove the signed-overflow
annotation, and reject a regressed nuw nsw multiply in the optimized IR.
Add a runtime marker test for 32x32 multiply, the 16x16 MPYU path, signed and
unsigned divide/remainder, and for sumto/squares compiled through the ordinary
tms-clang -O2 driver. The linked assembly is also checked for MPYS/MPYU/
DIVS/DIVU and for a surviving sumto loop.
arti