//build/toolchain/musl-host-gcc: implement

This is a cc_toolchain which runs on x86 systems with Linux/gcc and
targets Smalltown via static musl builds.

It is currently unused, but can be tested by trying to build any
cc_binary with
--crosstool_top=//build/toolchain/musl-host-gcc:musl_host_cc_suite .

Test Plan: This has been tested manually by running it against a simple cc_binary. Another revision on top of this will attempt to build mkfs.xfs with it.

X-Origin-Diff: phab/D623
GitOrigin-RevId: ebdf51ee76d9d5a7fd94725c66ef53783f787df7
diff --git a/build/toolchain/musl-host-gcc/sysroot.bzl b/build/toolchain/musl-host-gcc/sysroot.bzl
new file mode 100644
index 0000000..2f54ced
--- /dev/null
+++ b/build/toolchain/musl-host-gcc/sysroot.bzl
@@ -0,0 +1,26 @@
+#  Copyright 2020 The Monogon Project Authors.
+#
+#  SPDX-License-Identifier: Apache-2.0
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+load("//build/toolchain/musl-host-gcc:sysroot_repository.bzl", "musl_sysroot_rule")
+
+def musl_sysroot_repositories():
+    """
+    Provides an external repository that contains the extracted musl/linux sysroot.
+    """
+    musl_sysroot_rule(
+        name = "musl_sysroot",
+        snapshot = "//build/toolchain/musl-host-gcc:sysroot.tar.xz",
+    )