Do not autodetect C++ toolchain when BAZEL_DO_NOT_DETECT_CPP_TOOLCHAI…

…N=1 is present

This is useful e.g. when all C++ builds happen remotely and there's no C++
toolchain installed on the host machine.

Fixes bazelbuild#5133.

RELNOTES: None.
PiperOrigin-RevId: 196798471

tools/cpp/BUILD.empty

@@ -0,0 +1,48 @@
+# Copyright 2018 The Bazel Authors. All rights reserved.
+#
+# 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.
+
+package(default_visibility = ["//visibility:public"])
+
+cc_library(
+    name = "malloc",
+)
+
+cc_library(
+    name = "stl",
+)
+
+filegroup(
+    name = "empty",
+    srcs = [],
+)
+
+cc_toolchain_suite(
+    name = "toolchain",
+    toolchains = {
+        "local|local": ":local",
+    },
+)
+
+cc_toolchain(
+    name = "local",
+    all_files = ":empty",
+    compiler_files = ":empty",
+    cpu = "local",
+    dwp_files = ":empty",
+    dynamic_runtime_libs = [":empty"],
+    linker_files = ":empty",
+    objcopy_files = ":empty",
+    static_runtime_libs = [":empty"],
+    strip_files = ":empty",
+)

tools/cpp/CROSSTOOL.empty

@@ -0,0 +1,15 @@
+major_version: "local"
+minor_version: ""
+default_target_cpu: "local"
+
+toolchain {
+  abi_version: "local"
+  abi_libc_version: "local"
+  compiler: "local"
+  host_system_name: "local"
+  target_libc: "local"
+  target_cpu: "local"
+  target_system_name: "local"
+  toolchain_identifier: "local"
+}
+

tools/cpp/cc_configure.bzl

@@ -23,7 +23,10 @@ def cc_autoconf_impl(repository_ctx, overriden_tools = dict()):
       Label("@bazel_tools//tools/cpp:dummy_toolchain.bzl"), "dummy_toolchain.bzl")
   env = repository_ctx.os.environ
   cpu_value = get_cpu_value(repository_ctx)
-  if cpu_value == "freebsd":
+  if "BAZEL_DO_NOT_DETECT_CPP_TOOLCHAIN" in env and env["BAZEL_DO_NOT_DETECT_CPP_TOOLCHAIN"] == "1":
+    repository_ctx.symlink(Label("@bazel_tools//tools/cpp:CROSSTOOL.empty"), "CROSSTOOL")
+    repository_ctx.symlink(Label("@bazel_tools//tools/cpp:BUILD.empty"), "BUILD")
+  elif cpu_value == "freebsd":
     # This is defaulting to the static crosstool, we should eventually
     # autoconfigure this platform too.  Theorically, FreeBSD should be
     # straightforward to add but we cannot run it in a docker container so
@@ -53,6 +56,7 @@ cc_autoconf = repository_rule(
         "BAZEL_TARGET_LIBC",
         "BAZEL_TARGET_SYSTEM",
         "BAZEL_USE_CPP_ONLY_TOOLCHAIN",
+        "BAZEL_DO_NOT_DETECT_CPP_TOOLCHAIN",
         "BAZEL_USE_LLVM_NATIVE_COVERAGE",
         "BAZEL_VC",
         "BAZEL_VS",