pkg-config-wrapper: Provide autoconf macros

This fixes libarchive, and probably numerous other builds.

pkgs/build-support/pkg-config-wrapper/default.nix

···
       echo $pkg-config > $out/nix-support/orig-pkg-config
 
       wrap ${targetPrefix}pkg-config ${./pkg-config-wrapper.sh} "${getBin pkg-config}/bin/pkg-config"
+    ''
+    # symlink in share for autoconf to find macros
+
+    # TODO(@Ericson2314): in the future just make the unwrapped pkg-config a
+    # propagated dep once we can rely on downstream deps comming first in
+    # search paths. (https://github.com/NixOS/nixpkgs/pull/31414 took a crack
+    # at this.)
+    + ''
+      ln -s ${pkg-config}/share $out/share
     '';
 
   strictDeps = true;