transgui: fix transgui build on aarch64

Support for aarch64 was recencly added in fpc.
This regenerate the Makefile to include aarch64 support as the one in
the repository was too old to include it.

pkgs/applications/networking/p2p/transgui/default.nix

@@ -29,6 +29,7 @@ stdenv.mkDerivation rec {
   '';
 
   preBuild = ''
+    FPCDIR=${fpc}/lib/fpc/${fpc.version} fpcmake -w
     lazbuild -B transgui.lpr --lazarusdir=${lazarus}/share/lazarus
   '';