rpm: fix package sorting (RHBZ#1696822)

The sorting algorithm for RPMs sorted this way:
- before the packages with the higher versions
- among the packages with the version version, first noarch packages,
  then 64bit packages, and then 32bit packages
This was broken in at least two ways:
- the higher installed version may not be of the same host architecture
- if the host architecture is 32bit, and there is a 64bit package of a
  32bit installed one, the 64bit version was preferred

Instead:
- first sort by architecture, preferring noarch packages, and
  packages of the host architecture
- then sort by version

This way, the higher version of the host architecture is preferred,
otherwise the higher version of any foreign architecture is chosen.

src/ph_rpm.ml

@@ -172,9 +172,14 @@ let rpm_package_of_string str =
      * architecture.
      *)
     let cmp (pkg1, evr1) (pkg2, evr2) =
-      let i = rpm_vercmp evr2 evr2 in
+      let weight_of_arch = function
+        | "noarch" -> 100
+        | a when a = !rpm_arch -> 50
+        | _ -> 0
+      in
+      let i = compare (weight_of_arch pkg2.arch) (weight_of_arch pkg1.arch) in
       if i <> 0 then i
-      else compare_architecture pkg2.arch pkg1.arch
+      else rpm_vercmp evr2 evr2
     in
     let rpms = List.sort cmp rpms in
     fst (List.hd rpms)