I think this has nothing to do with Rcpp.
This is related to your system.
I show first lines of one tbd file below. It is just a text file. You can open it using a text editor.
--- !tapi-tbd-v3
archs: [ i386, x86_64, x86_64h ]
uuids: [ 'i386: 17321B27-67AB-3D26-B9DF-A69624B1C82B', 'x86_64: 358C547D-E227-3228-8218-62327F4605C8',
'x86_64h: 945E5C0A-86C5-336E-A64F-5BF06E78985A' ]
platform: macosx
install-name: /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation
current-version: 1452.23
compatibility-version: 150
exports:
- archs: [ i386 ]
symbols: [ '$ld$add$os10.5$.objc_class_name_NSObject', '$ld$add$os10.6$.objc_class_name_NSObject',
'$ld$add$os10.7$.objc_class_name_NSObject', '$ld$hide$os10.4$.objc_class_name_NSArray',
'$ld$hide$os10.4$.objc_class_name_NSCalendar', '$ld$hide$os10.4$.objc_class_name_NSData',
...
As I understand, the tbd file contains the version and location of the real library file. It is like a "link". (Just my personal understanding. Please correct me if this is wrong.)
After the upgrade of Xcode, your tbd file and real library are out of sync. Then you got the warning.
I think you can ignore this warning for now, since your compiler has fallen back and found the correct library.