graphics/R-cran-GDD: Fix build against math/R 4.6.0

R 4.6.0 removed the declaration of Rf_gsetVar from its installed
headers. Add a patch to replace the call to gsetVar() in GDD.c with
Rf_setVar(), making the implicit assignment to R_GlobalEnv explicit.

Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D56905