fix: elan: use relative paths in wrapper script

since 3.1.1, `elan` extracts to a temporary location and then moves to a
final location, this threw the wrapper script off. Updating the patch to
use paths relative to the wrapper script, so that it works independent
of absolute location.

pkgs/applications/science/logic/elan/0001-dynamically-patchelf-binaries.patch

@@ -2,7 +2,7 @@ diff --git a/src/elan-dist/src/component/package.rs b/src/elan-dist/src/componen
 index c51e76d..ae8159e 100644
 --- a/src/elan-dist/src/component/package.rs
 +++ b/src/elan-dist/src/component/package.rs
-@@ -56,6 +56,35 @@ fn unpack_without_first_dir<R: Read>(archive: &mut tar::Archive<R>, path: &Path)
+@@ -56,6 +56,37 @@ fn unpack_without_first_dir<R: Read>(archive: &mut tar::Archive<R>, path: &Path)
          entry
              .unpack(&full_path)
              .chain_err(|| ErrorKind::ExtractingPackage)?;
@@ -26,9 +26,11 @@ index c51e76d..ae8159e 100644
 +        use std::os::unix::fs::PermissionsExt;
 +        let new_path = dest_path.with_extension("orig");
 +        ::std::fs::rename(dest_path, &new_path)?;
-+        ::std::fs::write(dest_path, format!(r#"#! @shell@
-+LEAN_CC="${{LEAN_CC:-@cc@}}" exec -a "$0" {} "$@" -L {}/lib  # use bundled libraries, but not bundled compiler that doesn't know about NIX_LDFLAGS
-+"#, new_path.to_str().unwrap(), dest_path.parent().unwrap().parent().unwrap().to_str().unwrap()))?;
++        ::std::fs::write(dest_path, r#"#! @shell@
++dir="$(dirname "${BASH_SOURCE[0]}")"
++# use bundled libraries, but not bundled compiler that doesn't know about NIX_LDFLAGS
++LEAN_CC="${LEAN_CC:-@cc@}" exec -a "$0" "$dir/leanc.orig" "$@" -L"$dir/../lib"
++"#)?;
 +        ::std::fs::set_permissions(dest_path, ::std::fs::Permissions::from_mode(0o755))?;
 +    }
 +