cfg for linux, and remove test SO file

Author: Ellen Arteca

.gitignore

@@ -9,4 +9,4 @@ tex/*/out
 perf.data
 perf.data.old
 flamegraph.svg
-tests/external_C/libtestlib.so
+tests/extern-so/libtestlib.so

src/shims/ffi_support.rs

@@ -196,7 +196,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                     != lib_path.to_str().unwrap()
                 {
                     return Ok(false);
-                }
+                } 
             }
         }
 

tests/compiletest.rs

@@ -41,7 +41,7 @@ fn run_tests(mode: Mode, path: &str, target: Option<String>) -> Result<()> {
     }
 
     // If we're on linux, then build the shared object file for testing external C function calls.
-    if env::consts::OS == "linux" {
+    if cfg!(target_os = "linux") {
         let cc = option_env!("CC").unwrap_or("cc");
         Command::new(cc)
             .args([