Revert "Revert "Move toolchain registration into WORKSPACE (#5070)""

This reverts commit 1647371.

We previously introduced this in 5070 but reverted due to
incompatibilities with internal repo. Will couple this PR with another
internal PR to ensure compatibility between the 2.

.bazelrc

@@ -38,10 +38,9 @@ build:remote-shared --remote_download_minimal
 build:remote-shared --jobs=100
 build:remote-shared --verbose_failures
 build:remote-shared --platforms=@buildbuddy_toolchain//:platform_linux
-build:remote-shared --host_platform=@buildbuddy_toolchain//:platform_linux
-build:remote-shared --crosstool_top=@buildbuddy_toolchain//:ubuntu_cc_toolchain_suite
-build:remote-shared --extra_toolchains=@buildbuddy_toolchain//:ubuntu_cc_toolchain
-build:remote-shared --extra_toolchains=//:sh_toolchain
+build:remote-shared --extra_execution_platforms=@buildbuddy_toolchain//:platform_linux
+
+build --incompatible_enable_cc_toolchain_resolution
 
 # Build with --config=remote to use BuildBuddy RBE.
 build:remote --config=remote-shared
@@ -53,27 +52,9 @@ build:remote-dev --config=remote-shared
 build:remote-dev --config=cache-dev
 build:remote-dev --remote_executor=grpcs://buildbuddy.buildbuddy.dev
 
-# Build with --config=target-linux to
-#   - Tell Bazel to build binaries for linux
-#   - Tell Bazel to use Linux-compatible toolchains to build
-build:target-linux --cpu=k8
-build:target-linux --host_cpu=k8
-# Write linux-target build outputs in a separate directory from host build outputs.
-build:target-linux --experimental_platform_in_output_dir
-
-# Build with --config=remote-target-linux* to build on remote Linux Executors.
-# from non-Linux machines (e.g. MacOS).
-#
-# Example usage in user.bazelrc:
-#   build --remote_header=x-buildbuddy-api-key=<foo>
-#   build:x --config=remote-target-linux
-#
-# Then you could start building/testing remotely with MacOS with:
-#   bazel test --config=x //...
-build:remote-target-linux --config=target-linux
-build:remote-target-linux --config=remote
-build:remote-target-linux-dev --config=target-linux
-build:remote-target-linux-dev --config=remote-dev
+# Write build outputs in a platform-specific directory,
+# avoid outputs being wiped and rewritten when switching between platforms.
+build --experimental_platform_in_output_dir
 
 # Configuration used for GitHub actions-based CI
 build:ci --config=remote

BUILD

@@ -266,20 +266,3 @@ platform(
         "enable-vfs": "true",
     },
 )
-
-# TODO(bduffany): The sh_toolchain config here is a workaround for
-# https://github.com/aspect-build/rules_swc/issues/20
-# We should probably either move these to the buildbuddy-toolchain repo
-# or add a symlink from /usr/bin/bash -> /bin/bash to remove the need for these.
-load("@bazel_tools//tools/sh:sh_toolchain.bzl", "sh_toolchain")
-
-sh_toolchain(
-    name = "bash_rbe_ubuntu1604",
-    path = "/bin/bash",
-)
-
-toolchain(
-    name = "sh_toolchain",
-    toolchain = ":bash_rbe_ubuntu1604",
-    toolchain_type = "@bazel_tools//tools/sh:toolchain_type",
-)

WORKSPACE

@@ -461,3 +461,8 @@ load("@rules_proto//proto:repositories.bzl", "rules_proto_dependencies", "rules_
 rules_proto_dependencies()
 
 rules_proto_toolchains()
+
+register_toolchains(
+    "//toolchains:sh_toolchain",
+    "@buildbuddy_toolchain//:ubuntu_cc_toolchain",
+)

toolchains/BUILD

@@ -0,0 +1,19 @@
+# TODO(bduffany): The sh_toolchain config here is a workaround for
+# https://github.com/aspect-build/rules_swc/issues/20
+# We should probably either move these to the buildbuddy-toolchain repo
+# or add a symlink from /usr/bin/bash -> /bin/bash to remove the need for these.
+load("@bazel_tools//tools/sh:sh_toolchain.bzl", "sh_toolchain")
+
+sh_toolchain(
+    name = "bash_rbe_ubuntu1604",
+    path = "/bin/bash",
+)
+
+toolchain(
+    name = "sh_toolchain",
+    exec_compatible_with = [
+        "@platforms//os:linux",
+    ],
+    toolchain = ":bash_rbe_ubuntu1604",
+    toolchain_type = "@bazel_tools//tools/sh:toolchain_type",
+)