Simplify model number handling

We never use it as a number, so make it a string to begin with.

Author: joshtriplett

build.rs

@@ -540,7 +540,7 @@ mod c {
                 }
 
                 for (model_number, model_name) in
-                    &[(1, "relax"), (2, "acq"), (3, "rel"), (4, "acq_rel")]
+                    &[("1", "relax"), ("2", "acq"), ("3", "rel"), ("4", "acq_rel")]
                 {
                     let library_name = format!(
                         "liboutline_atomic_helper_{}_{}_{}.a",
@@ -552,7 +552,7 @@ mod c {
                     cfg.include(&builtins_dir)
                         .define(&format!("L_{}", instruction_type), None)
                         .define("SIZE", size.to_string().as_str())
-                        .define("MODEL", model_number.to_string().as_str())
+                        .define("MODEL", model_number)
                         .file(&outlined_atomics_file);
                     cfg.compile(&library_name);