I just tried a clean check-out of the project from the subversion repository, and was able to build each of the project targets with Xcode 4 without difficulty.
Likely there is an inconsistency in the target you are building of the STRIP_GTM_FETCH_LOGGING preprocessor flag, as some methods compile either in the GTMHTTPFetcher class or in the GTMHTTPFetcherLogging class depending on the value of that flag.