According to apple's release note, see the following note point.
Note:
Be aware of the following architectures issues when opening your
existing projects in Xcode 5.1:
- When building for all architectures, remove any explicit
architectures setting and use the default Standard Architectures
setting. For projects that were previously opted-in using “Standard
Architectures Including 64-Bit”, switch back to the “Standard
architectures” setting.
- When opening an existing project for the first time, Xcode 5.1 may
display a warning about the use of the Xcode 5.0 architectures
setting. Selecting the warning provides a workflow to revise the
setting.
- Projects not able to support 64-bit need to specifically set the
architectures build setting to not include 64-bit.
So you've to set architecture as below to support libs architecture.
Reference from this post.
Update: From May 15, you've to take build from 5.1.1, see this post.