There's a difference in effort of several orders of magnitude between "change a setting so the compiler doesn't emit multiplies" and "convince GCC/LLVM to add a special-case flag for one very rare chip, or maintain your own fork". The vendor's workaround is the "ideal" solution, but disabling multiplies is a lot more practical if you don't need the performance.

They also mention in the next sentence that they adopted the "correct" workaround (by providing a multiplication library function for the compiler to call).