stop excluding TERM env var on Unix

Author: RalfJung

README.md

@@ -282,9 +282,8 @@ environment variable. We first document the most relevant and most commonly used
   verbose. `hide` hides the warning entirely.
 * `-Zmiri-env-exclude=<var>` keeps the `var` environment variable isolated from the host so that it
   cannot be accessed by the program. Can be used multiple times to exclude several variables. The
-  `TERM` environment variable is excluded by default to [speed up the test
-  harness](https://github.com/rust-lang/miri/issues/1702). This has no effect unless
-  `-Zmiri-disable-isolation` is also set.
+  `TERM` environment variable is excluded by default in Windows to prevent the libtest harness from
+  accessing the file system. This has no effect unless `-Zmiri-disable-isolation` is also set.
 * `-Zmiri-env-forward=<var>` forwards the `var` environment variable to the interpreted program. Can
   be used multiple times to forward several variables. This takes precedence over
   `-Zmiri-env-exclude`: if a variable is both forwarded and exluced, it *will* get forwarded. This

src/shims/env.rs

@@ -42,10 +42,11 @@ impl<'tcx> EnvVars<'tcx> {
         config: &MiriConfig,
     ) -> InterpResult<'tcx> {
         let target_os = ecx.tcx.sess.target.os.as_ref();
-        // HACK: Exclude `TERM` var to avoid terminfo trying to open the termcap file.
-        // This is (a) very slow and (b) does not work on Windows.
         let mut excluded_env_vars = config.excluded_env_vars.clone();
-        excluded_env_vars.push("TERM".to_owned());
+        if target_os == "windows" {
+            // HACK: Exclude `TERM` var to avoid terminfo trying to open the termcap file.
+            excluded_env_vars.push("TERM".to_owned());
+        }
 
         // Skip the loop entirely if we don't want to forward anything.
         if ecx.machine.communicate() || !config.forwarded_env_vars.is_empty() {