Do not run `rustfmt` on the `compiler-builtins` subtree

This will get checked in the compiler-builtins repository. The rules are
slightly different from rust-lang/rust since `use_small_heuristics =
"Max"` tends to create difficult to read output with math-heavy code
(e.g.  multiple `if` statements with numbers are small enough that they
sometimes get collapsed into a single line).

0 files changed, 0 insertions, 0 deletions