exact versions for mavericks CRAN builds

hi folks,

i'm wanting to configure my macOS system so that it builds R packages 
using the same versions of the build tools as CRAN. my motivation is 
that i use some packages which make use of Rcpp, and i'd like my builds 
of them to be compatible with Rcpp from CRAN.

looking at the document here, describes the toolchain versions for lion 
(xcode 4.2):

http://r.research.att.com/tools/

but it seems likely to me that the newer mavericks (10.9+) builds on 
CRAN are built with something newer.

could someone confirm the version of xcode, et al. that i'll need to 
achieve c++ binary compatibility with the macOS binaries on CRAN?

with thanks

jonathon