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/development/tools/misc/pkg-config/requires-private.patch

@@ -0,0 +1,17 @@
+diff --git a/main.c b/main.c
+index b61ca34..5a420c2 100644
+--- a/main.c
++++ b/main.c
+@@ -602,10 +602,10 @@ main (int argc, char **argv)
+   else
+     disable_private_libs();
+ 
+-  /* honor Requires.private if any Cflags are requested or any static
++  /* honor Requires.private if any any static
+    * libs are requested */
+ 
+-  if (pkg_flags & CFLAGS_ANY || want_requires_private || want_exists ||
++  if (want_requires_private ||
+       (want_static_lib_list && (pkg_flags & LIBS_ANY)))
+     enable_requires_private();
+