libretro.pcsx2: avoid $NIX_BUILD_TOP

Using $NIX_BUILD_TOP in a Nix expression break under nix-shell (or when
using nativeBuildInputs = [ keepBuildTree ]), so let's avoid it.

Ref. https://github.com/NixOS/nixpkgs/issues/189691

Fixes: fe330c57da8bdd98 ("retroarchFull: fix pcsx2 core installation")

+1 -1
+1 -1
pkgs/applications/emulators/retroarch/cores.nix
··· 760 760 # causes redefinition of _FORTIFY_SOURCE 761 761 hardeningDisable = [ "fortify3" ]; 762 762 763 - postBuild = "cd $NIX_BUILD_TOP/source/build/pcsx2"; 763 + postBuild = "cd pcsx2"; 764 764 meta = { 765 765 description = "Port of PCSX2 to libretro"; 766 766 license = lib.licenses.gpl3Plus;