Rollup merge of #89468 - FabianWolff:issue-89358, r=jackh726

Report fatal lexer errors in `--cfg` command line arguments

Fixes #89358. The erroneous behavior was apparently introduced by `@Mark-Simulacrum` in a678e31911; the idea is to silence individual parser errors and instead emit one catch-all error message after parsing. However, for the example in #89358, a fatal lexer error is created here:
edebf77e00/compiler/rustc_parse/src/lexer/mod.rs (L340-L349)

This fatal error aborts the compilation, and so the call to `new_parser_from_source_str()` never returns and the catch-all error message is never emitted. I have therefore changed the `SilentEmitter` to silence only non-fatal errors; with my changes, for the rustc invocation described in #89358:
```sh
rustc --cfg "abc\""
```
I get the following output:
```
error[E0765]: unterminated double quote string
  |
  = note: this error occurred on the command line: `--cfg=abc"`
```

compiler/rustc_session/src/parse.rs

@@ -174,9 +174,14 @@ impl ParseSess {
         }
     }
 
-    pub fn with_silent_emitter() -> Self {
+    pub fn with_silent_emitter(fatal_note: Option<String>) -> Self {
         let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-        let handler = Handler::with_emitter(false, None, Box::new(SilentEmitter));
+        let fatal_handler = Handler::with_tty_emitter(ColorConfig::Auto, false, None, None);
+        let handler = Handler::with_emitter(
+            false,
+            None,
+            Box::new(SilentEmitter { fatal_handler, fatal_note }),
+        );
         ParseSess::with_span_handler(handler, sm)
     }