WIP switch to GenerateIntoSlashTemp to test whether that fixes issue when testing on CI.

Author: pnkfelix

tests/common/which_temp.rs

@@ -16,7 +16,13 @@ pub trait WhichTempDirectory {
 // Doing so has two drawbacks: 1. You need to clean-up the
 // generated directory yourself, and 2. You risk race conditions with
 // concurrent test runs.
-pub(crate) type WhichTempDir /*: WhichTempDirectory*/ = GenerateIntoFreshTemp;
+//
+// If you cange this to `GenerateIntoFreshTemp`, you get a fresh directory
+// (rooted at whatever is returned from `tempfile::tempdir()`). This reduces
+// race conditions (note that `cargo-bisect-rustc` still stores data in shared
+// locations like `~/.rustup`, so races can still arise) and allows the test
+// suite to clean up the directory itself.
+pub(crate) type WhichTempDir /*: WhichTempDirectory*/ = GenerateIntoSlashTemp;
 
 /// Using `GenerateIntoFreshTemp` yields a fresh directory in some
 /// system-dependent temporary space. This fresh directory will be autoamtically