debugging packages

I am debugging my package with printf statements and I would like to 
remove -O2 from the compiler options.

Why?  That should not affect the operation of printf (but if may well 
confuse source-code debuggers).

Can I do with a switch on ./configure or is it necessary to set the 
environment variables

If it is just your package, then the CFLAGS are taken from 
R_HOME/etc/Makeconf.  You can either edit that, or you can create a 
Makefile in your package's src directory which would give you complete 
control.  (We don't recommend the later for packages which are distributed 
as it is tricky to get cross-platform features right.)

Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595