Dear Rob,
thank you for this advice! Now R is compiling packages without any errors.
Then edit the FLIBS line in /usr/lib64/R/etc/Makeconf and remove all
the
references to the static libraries /builddir/..../lib*.a (as per the
errors above).
However, I wonder who added the newer zlib, curl etc. libraries to
compile the EPEL 6 R packages, as these require a newer kernel than being provided by
RHEL/CentOS 6...
Regards,
Martin