Build a new incr comp session dir from scratch every time

[bjorn3]

Rather than copying the old incr comp dir and then modifying it. This saves a copy/hardlink for files that are modified. And it removes the need for accurate work product tracking to avoid accumulating cruft, which is non-trivial. We don't accurately track the pre-LTO bitcode files for ThinLTO for example.

Based on #159225
Part of rust-lang/compiler-team#908

[rust-log-analyzer]

The job pr-check-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

error[E0308]: mismatched types
   --> src/librustdoc/doctest.rs:262:9
    |
261 |     } = match result {
    |               ------ this expression has type `(Result<Option<CreateRunnableDocTests>, String>, Option<...>)`
262 |         Ok(Some(collector)) => collector,
    |         ^^^^^^^^^^^^^^^^^^^ expected `(Result<Option<...>, ...>, ...)`, found `Result<_, _>`
    |
    = note: expected tuple `(std::result::Result<std::option::Option<CreateRunnableDocTests>, std::string::String>, std::option::Option<IncrCompSession>)`
                found enum `std::result::Result<_, _>`
    = note: the full name for the type has been written to '/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools/x86_64-unknown-linux-gnu/release/build/rustdoc/e2ade74941381a74/out/rustdoc-e2ade74941381a74.long-type-5676048101907234966.txt'
    = note: consider using `--verbose` to print the full type name to the console

error[E0308]: mismatched types
   --> src/librustdoc/doctest.rs:263:9
    |
261 |     } = match result {
    |               ------ this expression has type `(Result<Option<CreateRunnableDocTests>, String>, Option<...>)`
262 |         Ok(Some(collector)) => collector,
263 |         Ok(None) => return,
    |         ^^^^^^^^ expected `(Result<Option<...>, ...>, ...)`, found `Result<_, _>`
    |
    = note: expected tuple `(std::result::Result<std::option::Option<CreateRunnableDocTests>, std::string::String>, std::option::Option<IncrCompSession>)`
                found enum `std::result::Result<_, _>`
    = note: the full name for the type has been written to '/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools/x86_64-unknown-linux-gnu/release/build/rustdoc/e2ade74941381a74/out/rustdoc-e2ade74941381a74.long-type-5676048101907234966.txt'
    = note: consider using `--verbose` to print the full type name to the console

error[E0308]: mismatched types
   --> src/librustdoc/doctest.rs:264:9
    |
261 |     } = match result {
    |               ------ this expression has type `(Result<Option<CreateRunnableDocTests>, String>, Option<...>)`
...
264 |         Err(error) => {
    |         ^^^^^^^^^^ expected `(Result<Option<...>, ...>, ...)`, found `Result<_, _>`
    |
    = note: expected tuple `(std::result::Result<std::option::Option<CreateRunnableDocTests>, std::string::String>, std::option::Option<IncrCompSession>)`
                found enum `std::result::Result<_, _>`
    = note: the full name for the type has been written to '/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools/x86_64-unknown-linux-gnu/release/build/rustdoc/e2ade74941381a74/out/rustdoc-e2ade74941381a74.long-type-5676048101907234966.txt'
    = note: consider using `--verbose` to print the full type name to the console

error[E0277]: the `?` operator can only be used in a closure that returns `Result` or `Option` (or another type that implements `FromResidual`)
   --> src/librustdoc/lib.rs:858:27
    |
852 |                 interface::run_compiler(config, |compiler| {
    |                                                 ---------- this function should return `Result` or `Option` to accept `?`
...
858 |                         })?;
    |                           ^ cannot use the `?` operator in a closure that returns `(std::result::Result<(), _>, std::option::Option<IncrCompSession>)`

error[E0308]: mismatched types
   --> src/librustdoc/lib.rs:852:17
    |
850 |               return wrap_return(
    |                      ----------- arguments to this function are incorrect
851 |                   dcx,
852 | /                 interface::run_compiler(config, |compiler| {
853 | |                     // construct a phony "crate" without actually running the parser
854 | |                     // allows us to use other compiler infrastructure like dep-info
855 | |                     let file =
...   |
886 | |                     })
887 | |                 }),
    | |__________________^ expected `Result<(), String>`, found `(Result<(), _>, Option<IncrCompSession>)`
    |
    = note: expected enum `std::result::Result<(), std::string::String>`
              found tuple `(std::result::Result<(), _>, std::option::Option<IncrCompSession>)`
note: function defined here
   --> src/librustdoc/lib.rs:720:15
    |
720 | pub(crate) fn wrap_return(dcx: DiagCtxtHandle<'_>, res: Result<(), String>) {
    |               ^^^^^^^^^^^                          -----------------------

error[E0308]: mismatched types
   --> src/librustdoc/lib.rs:930:9
    |
930 | /         rustc_interface::create_and_enter_global_ctxt(compiler, krate, |tcx| {
931 | |             if sess.dcx().has_errors().is_some() {
932 | |                 sess.dcx().fatal("Compilation failed, aborting rustdoc");
...   |
995 | |         })
    | |          ^- help: consider using a semicolon here: `;`
    | |__________|
    |            expected `()`, found `((), Option<IncrCompSession>)`
    |
    = note: expected unit type `()`
                   found tuple `((), std::option::Option<IncrCompSession>)`
note: return type inferred to be `()` here
   --> src/librustdoc/lib.rs:926:13
    |
926 |             return;
    |             ^^^^^^