Move toolchain registration into WORKSPACE

Register our toolchains inside WORKSPACE.
Then enable automatic cc toolchain resolution for auto selection based
on platform compatibility.

.bazelrc

@@ -40,8 +40,8 @@ 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 --incompatible_enable_cc_toolchain_resolution
 
 # Build with --config=remote to use BuildBuddy RBE.
 build:remote --config=remote-shared

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",
+)