Add `alwayslink = 1` to fix undefined symbol linker errors for Swift for TensorFlow.
Context: https://github.com/apple/swift/pull/28438#issuecomment-557736052

Related Bazel change: https://github.com/bazelbuild/bazel/issues/7362
(`--incompatible_remove_legacy_whole_archive`)

Previously, libraries were wrapped in `--whole_archive` and `--no_whole_archive`
so that entire libraries were linked. With Bazel 1.0, libraries that export
unused symbols must be explicitly tagged with `alwayslink = 1`.

PiperOrigin-RevId: 282157053
Change-Id: Ica85797aeeb99e15402cdd06e61bbbf58011f141
diff --git a/tensorflow/c/BUILD b/tensorflow/c/BUILD
index a533fdd..fd58c1b 100644
--- a/tensorflow/c/BUILD
+++ b/tensorflow/c/BUILD
@@ -158,6 +158,7 @@
             "//tensorflow/core/kernels:logging_ops",
         ],
     }),
+    alwayslink = 1,
 )
 
 tf_cuda_library(