R ld library path fix

by default easybuild only adds $EBROOTR/lib64/ to LD_LIBRARY_PATH in R easyconfigs

some packages need $EBROOTR/lib64/R/lib in LD_LIBRARY_PATH to work correctly. As example, this one depends on this: https://github.com/hpcugent/easybuild-easyconfigs/pull/1149