Rollup merge of #77985 - cuviper:systemz-agr-clobbers-cc, r=nikic
Rollup merge of #77985 - cuviper:systemz-agr-clobbers-cc, r=nikic

llvm: backport SystemZ fix for AGR clobbers

Fixes #77382.

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