[Rd] Turn of -O2 during package build

[Saptarshi Guha]

Hello,
I'm using a Makevars.in file and running my code through gdb. I
understand i should turn of -O2, but R's makeconf overrides my
settings

/ln/meraki/custom/lib64/R/etc/Makeconf:112: warning: overriding
commands for target `.cc.o'

in Makevars.in

.cc.o:
	g++ -g ${PKG_CXXFLAGS} ${PKG_LIBS} ${RINC} ${RLIB} -c $< -o $@
Thank you
S.