Auto merge of #140842 - tmiasko:print-mono-items, r=saethlin

Remove mono item collection strategy override from -Zprint-mono-items

Previously `-Zprint-mono-items` would override the mono item collection
strategy. When debugging one doesn't want to change the behaviour, so
this was counter productive. Additionally, the produced behaviour was
artificial and might never arise without using the option in the first
place (`-Zprint-mono-items=eager` without `-Clink-dead-code`).  Finally,
the option was incorrectly marked as `UNTRACKED`.

Resolve those issues, by turning `-Zprint-mono-items` into a boolean
flag that prints results of mono item collection without changing the
behaviour of mono item collection.

For codegen-units test incorporate `-Zprint-mono-items` flag directly
into compiletest tool.

Test changes are mechanical. `-Zprint-mono-items=lazy` was removed
without additional changes, and `-Zprint-mono-items=eager` was turned
into `-Clink-dead-code`.  Linking dead code disables internalization, so
tests have been updated accordingly.

src/tests/compiletest.md

@@ -325,12 +325,8 @@ The tests in [`tests/codegen-units`] test the
 [monomorphization](../backend/monomorph.md) collector and CGU partitioning.
 
 These tests work by running `rustc` with a flag to print the result of the
-monomorphization collection pass, and then special annotations in the file are
-used to compare against that.
-
-Each test should be annotated with the `//@
-compile-flags:-Zprint-mono-items=VAL` directive with the appropriate `VAL` to
-instruct `rustc` to print the monomorphization information.
+monomorphization collection pass, i.e., `-Zprint-mono-items`, and then special
+annotations in the file are used to compare against that.
 
 Then, the test should be annotated with comments of the form `//~ MONO_ITEM
 name` where `name` is the monomorphized string printed by rustc like `fn <u32 as