Update conf-libelf opam package to include Macports, Alpine, and Ubuntu

Author: af-afk

packages/conf-libelf/conf-libelf.1.0.0/opam

@@ -6,14 +6,17 @@ homepage: "https://github.com/ocaml/opam-repository"
 bug-reports: "https://github.com/ocaml/opam-repository/issues"
 build: ["pkg-config" "--exists" "libelf"]
 depexts: [
-  ["libelf-dev"] {os-family = "debian"}
+  ["libelf-dev"] {os-family = "debian" | os-family = "ubuntu"}
   ["libelf"] {os-distribution = "arch"}
   ["dev-libs/libelf"] {os-distribution = "gentoo"}
   ["libelf"] {os = "freebsd"}
   ["libelf"] {os = "macos" & os-distribution = "homebrew"}
   ["libelf-devel"] {os = "win32" & os-distribution = "cygwinports"}
+  ["libelf"] {os = "alpine"}
+  ["libelf"] {os-distribution = "macports" & os = "macos"}
 ]
 synopsis: "Virtual package relying on libelf"
 description:
   "This package can only install if libelf is installed on the system."
+depends: ["conf-pkg-config" {build}]
 flags: conf