Work around missing tac command on macOS in PGO run-make test.
Work around missing tac command on macOS in PGO run-make test.

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