Fix typo around use of AVOID_VERSION

[jon-turney]

Fix typo in d4cc201e, which places $(AVOID_VERSION) between '-version-info' and '@VERSION_INFO@', leading to:

libtool: error: CURRENT '-avoid-version' must be a nonnegative integer libtool: error: '-avoid-version' is not valid version information

on those platforms where it's defined.