rustc_macros: don't limit the -Zmacro-backtrace suggestion to extern macros.

src/test/ui/span/E0204.stderr

@@ -15,6 +15,8 @@ LL | #[derive(Copy)]
 LL | struct Foo2<'a> {
 LL |     ty: &'a mut bool,
    |     ---------------- this field does not implement `Copy`
+   |
+   = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0204]: the trait `Copy` may not be implemented for this type
   --> $DIR/E0204.rs:17:6
@@ -33,6 +35,8 @@ LL | #[derive(Copy)]
 LL | enum EFoo2<'a> {
 LL |     Bar(&'a mut bool),
    |         ------------ this field does not implement `Copy`
+   |
+   = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 4 previous errors
 

src/test/ui/span/coerce-suggestions.stderr

@@ -49,7 +49,7 @@ error[E0308]: mismatched types
 LL |     s = format!("foo");
    |         ^^^^^^^^^^^^^^ expected `&mut std::string::String`, found struct `std::string::String`
    |
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 6 previous errors
 

src/test/ui/span/issue-33884.stderr

@@ -4,7 +4,7 @@ error[E0308]: mismatched types
 LL |     stream.write_fmt(format!("message received"))
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected struct `std::fmt::Arguments`, found struct `std::string::String`
    |
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error
 

src/test/ui/span/macro-span-replacement.stderr

@@ -13,4 +13,5 @@ note: the lint level is defined here
 LL | #![warn(unused)]
    |         ^^^^^^
    = note: `#[warn(dead_code)]` implied by `#[warn(unused)]`
+   = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/span/slice-borrow.stderr

@@ -10,7 +10,7 @@ LL |     y.use_ref();
    |     - borrow later used here
    |
    = note: consider using a `let` binding to create a longer lived value
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error