Allow file names to end with '>'

The `rustc_span::FileName` enum already differentiates between real
files and "fake" files such as `<anon>`. We do not need to artificially
forbid real file names from ending in `>`.

compiler/rustc_span/src/lib.rs

@@ -305,7 +305,6 @@ pub enum FileName {
 
 impl From<PathBuf> for FileName {
     fn from(p: PathBuf) -> Self {
-        assert!(!p.to_string_lossy().ends_with('>'));
         FileName::Real(RealFileName::LocalPath(p))
     }
 }