Auto merge of #30458 - fhahn:fix-warnings-tests-stdlib, r=sanxiyn

This PR siliences some warnings when compiling stdlib with --test. Mostly remove some unused imports and added a few `#[allow(..)]`.

I also marked some signal handling functions with `#[cfg(not(test))]`, because they are only called through `rt::lang_start`, which is also marked as  `#[cfg(not(test))]`

1 files changed, 2 insertions, 3 deletions

diff --git a/src/libstd/fs.rs b/src/libstd/fs.rs
index 715749f50d4..66e4c6013a4 100644
--- a/src/libstd/fs.rs
+++ b/src/libstd/fs.rs
@@ -1281,7 +1281,6 @@ mod tests {
     use io::{ErrorKind, SeekFrom};
     use path::PathBuf;
     use path::Path as Path2;
-    use os;
     use rand::{self, StdRng, Rng};
     use str;
 
@@ -1410,8 +1409,8 @@ mod tests {
         let message = "ten-four";
         let mut read_mem = [0; 4];
         let set_cursor = 4 as u64;
-        let mut tell_pos_pre_read;
-        let mut tell_pos_post_read;
+        let tell_pos_pre_read;
+        let tell_pos_post_read;
         let tmpdir = tmpdir();
         let filename = &tmpdir.join("file_rt_io_file_test_seeking.txt");
         {