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

src/test/ui/lint/lint-stability2.stderr

@@ -9,7 +9,7 @@ note: the lint level is defined here
    |
 LL | #![deny(deprecated)]
    |         ^^^^^^^^^^
-   = 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/lint/lint-stability3.stderr

@@ -9,7 +9,7 @@ note: the lint level is defined here
    |
 LL | #![deny(deprecated)]
    |         ^^^^^^^^^^
-   = 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/lint/lint-unsafe-code.stderr

@@ -90,6 +90,8 @@ LL |         unsafe {}
 ...
 LL |     unsafe_in_macro!()
    |     ------------------ in this macro invocation
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 14 previous errors
 

src/test/ui/lint/lints-in-foreign-macros.stderr

@@ -12,6 +12,7 @@ note: the lint level is defined here
    |
 LL | #![warn(unused_imports)]
    |         ^^^^^^^^^^^^^^
+   = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 warning: unused import: `std::string::ToString`
   --> $DIR/lints-in-foreign-macros.rs:16:18

src/test/ui/lint/test-inner-fn.stderr

@@ -5,12 +5,15 @@ LL |     #[test]
    |     ^^^^^^^
    |
    = note: requested on the command line with `-D unnameable-test-items`
+   = note: this error originates in an attribute macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: cannot test inner items
   --> $DIR/test-inner-fn.rs:13:9
    |
 LL |         #[test]
    |         ^^^^^^^
+   |
+   = note: this error originates in an attribute macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 2 previous errors
 

src/test/ui/lint/unreachable_pub-pub_crate.stderr

@@ -132,6 +132,7 @@ LL |     define_empty_struct_with_visibility!(pub, Fluorine);
    |     in this macro invocation
    |
    = help: or consider exporting it for use by other crates
+   = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 warning: unreachable `pub` item
   --> $DIR/unreachable_pub-pub_crate.rs:45:9

src/test/ui/lint/unreachable_pub.stderr

@@ -132,6 +132,7 @@ LL |     define_empty_struct_with_visibility!(pub, Fluorine);
    |     in this macro invocation
    |
    = help: or consider exporting it for use by other crates
+   = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 warning: unreachable `pub` item
   --> $DIR/unreachable_pub.rs:41:9