pkgconfig: rename to pkg-config (#55094)

Package attrs should map to the pname. It's confusing otherwise.

pkg-config is also the name used by most distributions:

Debian, Homebrew, Guix, OpenSuse

other distributions like FreeBSD ports, Fedora and Arch Linux call it
"pkgconf"

Waiting a few releases to make a tree-wide change to make it easier to
back-port things.

pkgs/top-level/all-packages.nix

@@ -8945,11 +8945,13 @@ in
 
   pkgconf = callPackage ../development/tools/misc/pkgconf {};
 
-  pkgconfig = callPackage ../development/tools/misc/pkgconfig {
+  pkg-config = callPackage ../development/tools/misc/pkg-config {
     fetchurl = fetchurlBoot;
   };
+  pkgconfig = pkg-config; # added 2018-02-02
 
-  pkgconfigUpstream = lowPrio (pkgconfig.override { vanilla = true; });
+  pkg-configUpstream = lowPrio (pkg-config.override { vanilla = true; });
+  pkgconfigUpstream = pkg-configUpstream; # added 2018-02-02
 
   postiats-utilities = callPackage ../development/tools/postiats-utilities {};