Please apply 8dcd71b45df3 to 5.4

Hi Greg and Sasha,

Please consider applying commit 8dcd71b45df3 ("powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp") to 5.4, as it resolves an error seen in that branch with a newer version of clang that looks for loops to turn into strlen(), which it is not allowed to do in this early code. It landed in 5.5 so it is in every other stable branch already. Please let me know if there are any issues.

Cheers, Nathan