Rollup merge of #80933 - rcvalle:fix-sysroot-option, r=nagisa
Rollup merge of #80933 - rcvalle:fix-sysroot-option, r=nagisa

Fix sysroot option not being honored across rustc

Change link_sanitizer_runtime() to check if the sanitizer library exists in the specified/session sysroot, and if it doesn't exist, use the default sysroot. (See #79253.)

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