Fix compilation warnings with gcc-12 - #100

FROM rocker/r-edge:gcc-12

RUN apt-get -y update
RUN apt-get -y install git
RUN R --slave -e "install.packages('knitr')"
RUN R --slave -e "install.packages('sass')"
RUN apt-get -y install libcurl4-openssl-dev
RUN R --slave -e "install.packages(c('testthat', 'rmarkdown', 'withr', 'shiny', 'curl'))"
RUN apt-get -y install pandoc
RUN mkdir /root/.R
RUN echo "CFLAGS +=              -O3 -Wall -pipe -pedantic -std=gnu99" > /root/.R/Makevars
RUN echo "CXXFLAGS +=            -O3 -Wall -pipe -Wno-unused -pedantic" >> /root/.R/Makevars

# git clone https://github.com/rstudio/sass && R CMD build --no-build-vignettes --no-manual sass && R CMD check sass*.tar.gz