How do I find out the version number of an installed library?

If you want to know what version is installed, just run:

rpm -q libxcb-devel

If you want to prevent upgrades to this package, you can add the package to the yum exclude configuration. Add the following to the main section in /etc/yum.conf:

exclude=libxcb-devel

The library version (e.g., in libxcb.so.1.1.0) very seldom tracks the package version, and is meant to track API changes.