Allow @emsdk to be imported in a non-x86_64 host. (#970)

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

bazel/BUILD

diff --git a/bazel/BUILD b/bazel/BUILD
index c84bf3f..0433f02 100644
--- a/bazel/BUILD
+++ b/bazel/BUILD
@@ -24,12 +24,15 @@
     ],
 )
 
+filegroup(name = "empty")
+
 alias(
     name = "binaries",
     actual = select({
         ":linux": "@emscripten_bin_linux//:all",
         ":macos": "@emscripten_bin_mac//:all",
         ":windows": "@emscripten_bin_win//:all",
+        "//conditions:default": ":empty",
     }),
 )
 
@@ -39,5 +42,6 @@
         ":linux": "@emscripten_npm_linux//:node_modules",
         ":macos": "@emscripten_npm_mac//:node_modules",
         ":windows": "@emscripten_npm_win//:node_modules",
+        "//conditions:default": ":empty",
     }),
 )