defaults.mak: Set LC_COLLATE=C.UTF-8 for reproducible sort order

With the 1.1.3 release we have seen some re-ordering of the
translation template and the translations. It turns out that
this is because sort sorts differently depending on the locale,
so let's force it to always sort in the C locale.

buildlib/defaults.mak

@@ -180,3 +180,6 @@ ifndef PARALLEL_RUN
   MAKEFLAGS += -j $(NUM_PROCS)
  endif
 endif
+
+# This makes sorting predictable
+export LC_COLLATE=C.UTF-8