gcc: Pull in Microblaze gcc atomic cas return value fix

This commit pulls in the fix for the Microblaze gcc atomic compare-and-swap
issue where atomic cas returns the inverse boolean value of what it should.
Furthermore, it pulls in the fix for atomic_compare_exchange where compiler
optimisations end up generating incorrect assembly.
https://github.com/zephyrproject-rtos/gcc/21

Signed-off-by: Alp Sayin <[email protected]>