Add CI config to test on RBE. (#1638)

* Add CI config to test on RBE.

* Disable BAZEL_DO_NOT_DETECT_CPP_TOOLCHAIN.

This is set by default in the rbe_ubuntu1604 platform, but tests in this
repo need this to be disabled.

* Skip tests that are not RBE compatible.

.bazelci/presubmit.yml

@@ -15,3 +15,18 @@ platforms:
     - "..."
     test_targets:
     - "..."
+  rbe_ubuntu1604:
+    build_targets:
+    - "..."
+    test_flags:
+    # Some tests depend on this feature being disabled. However, because it's
+    # enabled by default in the rbe_ubuntu1604 platform, we cannot simply remove
+    # this flag here, we have to explicitly override it with 0.
+    - "--action_env=BAZEL_DO_NOT_DETECT_CPP_TOOLCHAIN=0"
+    test_targets:
+    - "--"
+    - "..."
+    - "-//:vet"
+    - "-//tests/core/go_path:go_path_test"
+    - "-//tests/core/stdlib:buildid_test"
+    - "-@com_github_mattn_go_sqlite3//:go_default_test"

WORKSPACE

@@ -1,5 +1,6 @@
 workspace(name = "io_bazel_rules_go")
 
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 load("@io_bazel_rules_go//go:def.bzl", "go_rules_dependencies", "go_register_toolchains")
 load("@io_bazel_rules_go//proto:def.bzl", "proto_register_toolchains")
 
@@ -39,3 +40,12 @@ llvm_toolchain(
     name = "llvm_toolchain",
     llvm_version = "6.0.0",
 )
+
+http_archive(
+    name = "bazel_toolchains",
+    sha256 = "7938215442cc96b1a16809f4643db14af7d91c3ef1e98d39593bb46862204537",
+    strip_prefix = "bazel-toolchains-809c13c3a96966f63c7a43c586cb4e72589184b6",
+    urls = [
+        "https://github.com/bazelbuild/bazel-toolchains/archive/809c13c3a96966f63c7a43c586cb4e72589184b6.tar.gz",
+    ],
+)