Unbreak gv (fixes #34841) (#40658)

It appears that without pkgconfig, the build process misdetects some features, resulting in gv to segfault immediately on startup.

The fix was adopted from https://github.com/Homebrew/legacy-homebrew/issues/18555#issuecomment-15074618.

Changed files
+1 -1
pkgs
applications
misc
+1 -1
pkgs/applications/misc/gv/default.nix
···
Xaw3d
ghostscriptX
perl
-
] ++ stdenv.lib.optionals stdenv.isDarwin [
pkgconfig
libiconv
];
···
Xaw3d
ghostscriptX
perl
pkgconfig
+
] ++ stdenv.lib.optionals stdenv.isDarwin [
libiconv
];