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).
The company selling the chip can create a fork. They are typically the ones providing all of the sdks for you to use in order to use it, flash it, debug it, etc.