Fix libkml breaks due to automake update

The new version of autotools that was committed https://github.com/mxcl/homebrew/commit/1e5eb62094b1a67a398190cc237110913b80111c is being more strict about using older autoconf/autotools directives. It is failing to `build libkml --HEAD`. This is more critical than it sounds because `libkml --HEAD` is the only way to get GDAL support for kmz and contemporary kml features.