Switch build-deps from gcc-10 to gcc-12. Closes: #1022184

Switch build-deps from gcc-10 to gcc-12. Closes: #1022184

Also needs backports from upstream commits to fix warnings/errors
from using gcc 12:

be8eb0eed util/mkimage: Fix dangling pointer may be used error
acffb8148 build: Fix -Werror=array-bounds array subscript 0 is outside array bounds
3ce13d974 lib/reed_solomon: Fix array subscript 0 is outside array bounds