Resolve clippy::single_char_pattern

    error: single-character string constant used as pattern
       --> src/helpers.rs:805:36
        |
    805 |         .map(|crates| crates.split(",").map(|krate| krate.to_string()).collect::<Vec<_>>())
        |                                    ^^^ help: try using a `char` instead: `','`
        |
        = note: `-D clippy::single-char-pattern` implied by `-D clippy::all`
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#single_char_pattern

Author: dtolnay

src/helpers.rs

@@ -802,7 +802,7 @@ pub fn get_local_crates(tcx: &TyCtxt<'_>) -> Vec<CrateNum> {
     // Convert the local crate names from the passed-in config into CrateNums so that they can
     // be looked up quickly during execution
     let local_crate_names = std::env::var("MIRI_LOCAL_CRATES")
-        .map(|crates| crates.split(",").map(|krate| krate.to_string()).collect::<Vec<_>>())
+        .map(|crates| crates.split(',').map(|krate| krate.to_string()).collect::<Vec<_>>())
         .unwrap_or_default();
     let mut local_crates = Vec::new();
     for &crate_num in tcx.crates(()) {

src/lib.rs

@@ -20,7 +20,6 @@
     clippy::manual_map,
     clippy::needless_lifetimes,
     clippy::new_without_default,
-    clippy::single_char_pattern,
     clippy::single_match,
     clippy::unnecessary_mut_passed,
     clippy::useless_conversion,