You must re-compile your project in XE4, using XE4's VCL.
If by "XE3 VCL" you are actually referring to third-party VCL components, then they need to be compiled and installed in XE4 before they can be used in XE4 projects.
This is true of just about every Delphi version (D2007 being the only exception, as it was binary compatible with D2006).