Fix iOS cross compilation and enable test (#2099)

Updates #2079
diff --git a/go/private/platforms.bzl b/go/private/platforms.bzl
index 55319ff..45dd4af 100644
--- a/go/private/platforms.bzl
+++ b/go/private/platforms.bzl
@@ -168,7 +168,7 @@
         platforms.append(struct(
             name = "ios_" + goarch,
             goos = "darwin",
-            goarch = "goarch",
+            goarch = goarch,
             constraints = constraints,
             cgo = False,
         ))
@@ -176,7 +176,7 @@
         platforms.append(struct(
             name = "ios_" + goarch + "_cgo",
             goos = "darwin",
-            goarch = "goarch",
+            goarch = goarch,
             constraints = constraints,
             cgo = True,
         ))
diff --git a/tests/core/cross/BUILD.bazel b/tests/core/cross/BUILD.bazel
index a1b932c..3666257 100644
--- a/tests/core/cross/BUILD.bazel
+++ b/tests/core/cross/BUILD.bazel
@@ -50,36 +50,33 @@
     deps = ["//go/tools/bazel:go_default_library"],
 )
 
-# TODO(#2090): enable test when cgo toolchains are sorted out. This won't
-# build on non-darwin platforms if we need a C/C++ toolchain.
+bazel_test(
+    name = "ios_select_test",
+    args = ["--platforms=@io_bazel_rules_go//go/toolchain:ios_amd64"],
+    command = "build",
+    targets = [":ios_lib"],
+)
 
-# bazel_test(
-#     name = "ios_select_test",
-#     args = ["--platforms=@io_bazel_rules_go//go/toolchain:ios_amd64"],
-#     command = "build",
-#     targets = [":ios_lib"],
-# )
+go_library(
+    name = "use_ios_lib",
+    importpath = "github.com/bazelbuild/rules_go/tests/core/cross/use_ios_lib",
+    deps = select({
+        ":is_osx": [":ios_lib"],
+        "//conditions:default": [],
+    }),
+)
 
-# go_library(
-#     name = "use_ios_lib",
-#     importpath = "github.com/bazelbuild/rules_go/tests/core/cross/use_ios_lib",
-#     deps = select({
-#         ":is_osx": [":ios_lib"],
-#         "//conditions:default": [],
-#     }),
-# )
+config_setting(
+    name = "is_osx",
+    constraint_values = ["@bazel_tools//platforms:osx"],
+)
 
-# config_setting(
-#     name = "is_osx",
-#     constraint_values = ["@bazel_tools//platforms:osx"],
-# )
-
-# go_library(
-#     name = "ios_lib",
-#     srcs = select({
-#         "@io_bazel_rules_go//go/platform:darwin": ["ios_good.go"],
-#         "//conditions:default": ["ios_bad.go"],
-#     }),
-#     importpath = "github.com/bazelbuild/rules_go/tests/core/cross/ios_lib",
-#     tags = ["manual"],
-# )
+go_library(
+    name = "ios_lib",
+    srcs = select({
+        "@io_bazel_rules_go//go/platform:darwin": ["ios_good.go"],
+        "//conditions:default": ["ios_bad.go"],
+    }),
+    importpath = "github.com/bazelbuild/rules_go/tests/core/cross/ios_lib",
+    tags = ["manual"],
+)