build,tools: do not force codesign prefix

Allow passing the prefix in via the PKGDIR env var. This will allow us
to use this same script to codesign the binary tarball.

PR-URL: https://github.com/nodejs/node/pull/14179
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

tools/osx-codesign.sh

@@ -8,4 +8,4 @@ if [ "X$SIGN" == "X" ]; then
   exit 0
 fi
 
-codesign -s "$SIGN" "$PKGDIR"/usr/local/bin/node
+codesign -s "$SIGN" "$PKGDIR"/bin/node