Clean up the posix source files in rlz/

This is a preliminary change to remove the posix source exclusion
filter in a future commit.

Bug: 835405
Change-Id: I6f9ca7dda2679bf7b4b1bf896ab734b35e5a3f3b
Reviewed-on: https://chromium-review.googlesource.com/1022330
Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552473}

rlz/BUILD.gn

@@ -49,8 +49,6 @@ if (!is_android) {
       "lib/financial_ping.h",
       "lib/machine_id.cc",
       "lib/machine_id.h",
-      "lib/recursive_cross_process_lock_posix.cc",
-      "lib/recursive_cross_process_lock_posix.h",
       "lib/rlz_lib.cc",
       "lib/rlz_lib.h",
       "lib/rlz_lib_clear.cc",
@@ -85,6 +83,12 @@ if (!is_android) {
       "//url",
     ]
 
+    if (is_posix) {
+      sources += [
+        "lib/recursive_cross_process_lock_posix.cc",
+        "lib/recursive_cross_process_lock_posix.h",
+      ]
+    }
     if (is_chromeos) {
       deps += [ "//chromeos" ]
     }