setup-hooks/strip: resolve/uniq symlinks before stripping

Before the change the hook had a chance to run `strip` against the same
file using multiple link paths. In case of `gcc` `libgcc.a` was stripped
multiple times in parallel and produces corrupted archive.

The change runs inputs via `realpath | uniq` to make sure we don't
attempt to strip the same files multiple times.

pkgs/build-support/setup-hooks/strip.sh

@@ -68,6 +68,11 @@ stripDirs() {
         striperr="$(mktemp 'striperr.XXXXXX')"
         # Do not strip lib/debug. This is a directory used by setup-hooks/separate-debug-info.sh.
         find $paths -type f -a '!' -path "$prefix/lib/debug/*" -print0 |
+            # Make sure we process files under symlinks only once. Otherwise
+            # 'strip` can corrupt files when writes to them in parallel:
+            #   https://github.com/NixOS/nixpkgs/issues/246147#issuecomment-1657072039
+            xargs -r -0 -n1 -- realpath -z | sort -u -z |
+
             xargs -r -0 -n1 -P "$NIX_BUILD_CORES" -- $cmd $stripFlags 2>"$striperr" || exit_code=$?
         # xargs exits with status code 123 if some but not all of the
         # processes fail. We don't care if some of the files couldn't