[pod] Whitelist pods for configurations
[pod] Whitelist pods for configurations

An option to only link a specific pod to the target when building in a specific configuration.
The exact syntax is still TBD, pending discussion in https://github.com/CocoaPods/CocoaPods/pull/1668
which implements the corresponding functionality.

Ashton-W/Core,k0nserv/Core,CocoaPods/Core,brianmichel/Core,dnkoutso/Core,gabro/Core,dacaiguoguogmail/Core,AdamCampbell/Core