Eliminate ydbposix.xc.in & replace with ydbposix.xc
The only purpose of the
ydbposix.xc.in file is to replace the
@ydb_install_dir@ at the top with the actual path to the plugin. While this was needed before GT.M allowed environment variables in
.xc files, it is no longer needed, and the first line should just read
$ydb_dist/plugin/libydbposix.so. So, the
ydbposix.xc.in can be replaced with a
ydbposix.xc and the build process appropriately simplified to reflect this.