The complete error I got was:

C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v14.0\ReportingServices\Microsoft.ReportingServices.targets(24, 2): error MSB4062: The "Microsoft.Reporting.RdlCompile" task could not be loaded from the assembly Microsoft.ReportViewer.WebForms, Version=12.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91. Could not load file or assembly 'Microsoft.ReportViewer.WebForms, Version=12.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91' or one of its dependencies. The system cannot find the file specified. Confirm that the declaration is correct, that the assembly and all its dependencies are available, and that the task contains a public class that implements Microsoft.Build.Framework.ITask.

To solve this, first download and install ENU\x64\SQLSysClrTypes.msi (or pick the x86 version if that fits your setup) from the promt on Microsoft SQL Server 2014 Feature Pack. This is a prerequisite for installing the Report Viewer 2015 Runtime which you'll do next. The  Report Viewer runtime is what the error is pointing at.

This is relevant if you're building your EPiServer Commerce project with the Commerce Manager from TeamCity.