Automatically use system's crypto library on Linux/s390x. (#220)

BoringSSL doesn't support Linux/s390x.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

Author: PiotrSikora

bazel/BUILD

@@ -1,3 +1,5 @@
+load("@bazel_skylib//lib:selects.bzl", "selects")
+
 config_setting(
     name = "runtime_v8",
     values = {"define": "runtime=v8"},
@@ -19,6 +21,19 @@ config_setting(
 )
 
 config_setting(
-    name = "crypto_system",
+    name = "requested_crypto_system",
     values = {"define": "crypto=system"},
 )
+
+config_setting(
+    name = "linux_s390x",
+    values = {"cpu": "s390x"},
+)
+
+selects.config_setting_group(
+    name = "crypto_system",
+    match_any = [
+        ":requested_crypto_system",
+        ":linux_s390x",
+    ],
+)

bazel/repositories.bzl

@@ -174,3 +174,12 @@ def proxy_wasm_cpp_host_repositories():
         strip_prefix = "rules_python-0.6.0",
         url = "https://github.com/bazelbuild/rules_python/archive/0.6.0.tar.gz",
     )
+
+    http_archive(
+        name = "bazel_skylib",
+        urls = [
+            "https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/releases/download/1.1.1/bazel-skylib-1.1.1.tar.gz",
+            "https://github.com/bazelbuild/bazel-skylib/releases/download/1.1.1/bazel-skylib-1.1.1.tar.gz",
+        ],
+        sha256 = "c6966ec828da198c5d9adbaa94c05e3a1c7f21bd012a0b29ba8ddbccb2c93b0d",
+    )