Set debuginfo-level = "line-tables-only" for compiler profile

This profile has only undergone minimal tweaks since it was originally
drafted. I asked a number of compiler contributors and they said they
set rust.debug explicitly. This was even true for one contributor that
set `rust.debug` = false! Almost everyone seems slightly surprised that
`rust.debug = true` is not the default.

However, adding full debuginfo at this level costs multiple gigabytes!
We can still get much better debuginfo by setting "line-tables-only"
at the cost of only 150~200 MB.

Author: workingjubilee

src/bootstrap/defaults/config.compiler.toml

@@ -8,6 +8,8 @@ compiler-docs = true
 # where adding `debug!()` appears to do nothing.
 # However, it makes running the compiler slightly slower.
 debug-logging = true
+# Get actually-useful information from backtraces, profiling, etc. with minimal added bytes
+debuginfo-level = "line-tables-only"
 # This greatly increases the speed of rebuilds, especially when there are only minor changes. However, it makes the initial build slightly slower.
 incremental = true
 # Print backtrace on internal compiler errors during bootstrap

src/bootstrap/src/utils/change_tracker.rs

@@ -175,4 +175,9 @@ pub const CONFIG_CHANGE_HISTORY: &[ChangeInfo] = &[
         severity: ChangeSeverity::Warning,
         summary: "The deprecated field `changelog-seen` has been removed. Using that field in `config.toml` from now on will result in breakage.",
     },
+    ChangeInfo {
+        change_id: 123337,
+        severity: ChangeSeverity::Info,
+        summary: r#"The compiler profile now defaults to rust.debuginfo-level = "line-tables-only""#,
+    },
 ];