Patch around it in microcode (applied by the OS or BIOS on every boot; releasable as an OS update), disable the related CPU feature if possible (twiddling bits during OS initialization), or trap any related exception the CPU throws, detect the bug's condition, and patch up the running task's state from the exception handler (again, another OS update).
If all else fails, issue a product recall or downplay the bug's severity.
or recall all CPUs and replace them with new repaired ones. That's what they do in Wonderland. :D
On a more serious note, I wonder what auto manufacturers do. (There are many CPUs in modern automobiles, and auto manufacturers are often compelled to do recalls.)
Traditional embedded devices (i.e. not smartphones) tend to use very mature and well understood CPUs. Moreso for things holding life and propery like cars. If a bug does occur and cause a crash, normally a watchdog timer will reset the CPU quickly enough to avoid unrecoverable problems.
They're certainly not pushing the bleeding edge at all like the 3 GHz desktop/laptop processors.
If all else fails, issue a product recall or downplay the bug's severity.