Auto merge of #78039 - tmiasko:unreachable-block, r=Mark-Simulacrum
Auto merge of #78039 - tmiasko:unreachable-block, r=Mark-Simulacrum

Remove unused cached_unreachable_block from MIR builder

aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust