CC seems hardcoded to 'gcc' ?

[CdeMills]

Hello, I'm using clang under CentOS-8 linux to compile R packages. To this end, I created ~/R/Makevars with: CC=clang CXX=clang++ While performing install.packages('tidyverse'), your package was the only one compiled with gcc. Is there a reason ? If not, is gcc hardcoded as compiler ? TIA Pascal Dupuis