Prepare .bzl files to the new semantics of += on lists

In the future += on lists will work like .extend (by mutating the list) instead
of copying the list items to a new list (current behavior). Some .bzl files
need to be cleaned up to be compatible with both behaviors.

PiperOrigin-RevId: 165528261

tools/build_defs/pkg/pkg.bzl

diff --git a/tools/build_defs/pkg/pkg.bzl b/tools/build_defs/pkg/pkg.bzl
index 272b1ae..f5a17df 100644
--- a/tools/build_defs/pkg/pkg.bzl
+++ b/tools/build_defs/pkg/pkg.bzl
@@ -31,7 +31,7 @@
       "--owner=" + ctx.attr.owner,
       "--owner_name=" + ctx.attr.ownername,
       ]
-  file_inputs = ctx.files.srcs
+  file_inputs = ctx.files.srcs[:]
   args += ["--file=%s=%s" % (f.path, dest_path(f, data_path))
            for f in ctx.files.srcs]
   for target, f_dest_path in ctx.attr.files.items():