scripts: tweak rust-bootstrap+rust-host in cros_setup_toolchains

dev-lang/rust-host is a toolchain package that dev-lang/rust depends on.
It never requires cross-compilers.

While I'm in the area, move rust-bootstrap to HOST_PACKAGES; that
shouldn't require cross-compilers, either.

BUG=b:234615110
TEST=CQ

Change-Id: I5d39ff1f5d8df4ac03bdcb4e5fc7d9ff6c1e40a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3684154
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
Commit-Queue: George Burgess <gbiv@chromium.org>
Reviewed-by: Cindy Lin <xcl@google.com>
Tested-by: George Burgess <gbiv@chromium.org>
Reviewed-by: Allen Webb <allenwebb@google.com>
diff --git a/scripts/cros_setup_toolchains.py b/scripts/cros_setup_toolchains.py
index da8dab4..cf96081 100644
--- a/scripts/cros_setup_toolchains.py
+++ b/scripts/cros_setup_toolchains.py
@@ -53,6 +53,8 @@
 # want crossdev managing /etc/portage config files for the sdk
 HOST_PACKAGES = (
     'dev-lang/go',
+    'dev-lang/rust-bootstrap',
+    'dev-lang/rust-host',
     'dev-libs/elfutils',
     'sys-devel/binutils',
     'sys-devel/gcc',
@@ -69,7 +71,6 @@
 # build), so we have to delay their installation.
 HOST_POST_CROSS_PACKAGES = (
     'dev-lang/rust',
-    'dev-lang/rust-bootstrap',
     'virtual/target-sdk-post-cross',
     'dev-embedded/coreboot-sdk',
     'dev-embedded/hps-sdk',