Move the standard library to a separate workspace

This ensures that the Cargo.lock packaged for it in the rust-src
component is up-to-date, allowing rust-analyzer to run cargo metadata on
the standard library even when the rust-src component is stored in a
read-only location as is necessary for loading crates.io dependencies of
the standard library.

This also simplifies tidy's license check for runtime dependencies as it
can now look at all entries in library/Cargo.lock without having to
filter for just the dependencies of runtime crates. In addition this
allows removing an exception in check_runtime_license_exceptions that
was necessary due to the compiler enabling a feature on the object crate
which pulls in a dependency not allowed for the standard library.

While cargo workspaces normally enable dependencies of multiple targets
to be reused, for the standard library we do not want this reusing to
prevent conflicts between dependencies of the sysroot and of tools that
are built using this sysroot. For this reason we already use an unstable
cargo feature to ensure that any dependencies which would otherwise be
shared get a different -Cmetadata argument as well as using separate
build dirs.

This doesn't change the situation around vendoring. We already have
several cargo workspaces that need to be vendored. Adding another one
doesn't change much.

There are also no cargo profiles that are shared between the root
workspace and the library workspace anyway, so it doesn't add any extra
work when changing cargo profiles.

Cargo.toml

@@ -2,8 +2,6 @@
 resolver = "1"
 members = [
   "compiler/rustc",
-  "library/std",
-  "library/sysroot",
   "src/etc/test-float-parse",
   "src/rustdoc-json-types",
   "src/tools/build_helper",
@@ -61,23 +59,8 @@ exclude = [
   # not all `Cargo.toml` files are available, so we exclude the `x` binary,
   # so it can be invoked before the current checkout is set up.
   "src/tools/x",
-  # stdarch has its own Cargo workspace
-  "library/stdarch",
 ]
 
-[profile.release.package.compiler_builtins]
-# For compiler-builtins we always use a high number of codegen units.
-# The goal here is to place every single intrinsic into its own object
-# file to avoid symbol clashes with the system libgcc if possible. Note
-# that this number doesn't actually produce this many object files, we
-# just don't create more than this number of object files.
-#
-# It's a bit of a bummer that we have to pass this here, unfortunately.
-# Ideally this would be specified through an env var to Cargo so Cargo
-# knows how many CGUs are for this specific crate, but for now
-# per-crate configuration isn't specifiable in the environment.
-codegen-units = 10000
-
 [profile.release.package.rustc-rayon-core]
 # The rustc fork of Rayon has deadlock detection code which intermittently
 # causes overflows in the CI (see https://github.com/rust-lang/rust/issues/90227)
@@ -85,19 +68,6 @@ codegen-units = 10000
 # FIXME: This workaround should be removed once #90227 is fixed.
 overflow-checks = false
 
-# These dependencies of the standard library implement symbolication for
-# backtraces on most platforms. Their debuginfo causes both linking to be slower
-# (more data to chew through) and binaries to be larger without really all that
-# much benefit. This section turns them all to down to have no debuginfo which
-# helps to improve link times a little bit.
-[profile.release.package]
-addr2line.debug = 0
-adler.debug = 0
-gimli.debug = 0
-miniz_oxide.debug = 0
-object.debug = 0
-rustc-demangle.debug = 0
-
 # These are very thin wrappers around executing lld with the right binary name.
 # Basically nothing within them can go wrong without having been explicitly logged anyway.
 # We ship these in every rustc tarball and even after compression they add up
@@ -120,10 +90,3 @@ codegen-units = 1
 # FIXME: LTO cannot be enabled for binaries in a workspace
 # <https://github.com/rust-lang/cargo/issues/9330>
 # lto = true
-
-[patch.crates-io]
-# See comments in `library/rustc-std-workspace-core/README.md` for what's going on
-# here
-rustc-std-workspace-core = { path = 'library/rustc-std-workspace-core' }
-rustc-std-workspace-alloc = { path = 'library/rustc-std-workspace-alloc' }
-rustc-std-workspace-std = { path = 'library/rustc-std-workspace-std' }