[Rd] LCONS undefined for R_NO_REMAP

[Jeroen Ooms]

Rinternals.h has:

#define CONS(a, b) cons((a), (b))
#define LCONS(a, b) lcons((a), (b))

However these are undefined when we compile with -DR_NO_REMAP. Maybe
it's safer to define these using Rf_cons() and Rf_lcons() instead?