Tomcat jdbc pool is a standalone lib comes with tomcat 7.0.19
It has a much better concurrency performance compares those "old guys", (DBCP, c3p0, as you can name)
It can be used outside of tomcat, it has one dependence tomcat-juli.jar. By default if the build script detected the target app-server is tomcat, it won't deploy the tomcat-juli.jar shipped with liferay, but try to directly use the target tomcat one. If for some reason, you are working on an old version tomcat which can not provide a valid tomcat-juli.jar, you can configure liferay to force deploy the shipped tomcat-juli.jar in build.properties
For non-tomcat app-servers, tomcat-juli.jar will be automatically deployed.