[cdc_rsync] [cdc_rsync_server] Add build ID

Build id is an optional unique identifier specified during cdc_rsync build via CDC_BUILD_VERSION definition.
If build id specified on both client and server components it will be used to check the version of server component instead of file size + modified time.

common/BUILD

@@ -44,6 +44,11 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "build_version",
+    hdrs = ["build_version.h"],
+)
+
 cc_library(
     name = "dir_iter",
     srcs = ["dir_iter.cc"],
@@ -395,6 +400,7 @@ cc_library(
         ":path",
         ":platform",
         ":status",
+        "//common:build_version",
         "@com_google_absl//absl/status",
         "@com_google_absl//absl/strings:str_format",
     ],