Propagate alwayslink in the grpc_cc_library build rule template.

bazel/grpc_build_system.bzl

@@ -25,7 +25,8 @@
 
 def grpc_cc_library(name, srcs = [], public_hdrs = [], hdrs = [],
                     external_deps = [], deps = [], standalone = False,
-                    language = "C++", testonly = False, visibility = None):
+                    language = "C++", testonly = False, visibility = None,
+                    alwayslink = 0):
   copts = []
   if language.upper() == "C":
     copts = ["-std=c99"]
@@ -40,7 +41,8 @@ def grpc_cc_library(name, srcs = [], public_hdrs = [], hdrs = [],
     linkopts = ["-pthread"],
     includes = [
         "include"
-    ]
+    ],
+    alwayslink = alwayslink,
   )
 
 def grpc_proto_plugin(name, srcs = [], deps = []):