v8-3_16_14 tweaks for the build on darwin

The build was originally failing due to a missing libtool. Trying to add
the buildInput "libtool" did not work out, since a few command line
arguments are not supported. I've applied the same workaround as for
"xcodebuild".

The second change is about the install step, where the path of
"libv8.dylib" was just slightly different.