While working on MONGOCRYPT-512 it became evident that it would be very helpful to have -Wall -Werror as default compile options in Evergreen builds. It seems that this was done once before (MONGOCRYPT-103, commit 05bb025ffae269fe47d41e81636d98b438daf4c8) but that somehow it was changed and we no longer have this.

Note that as part of MONGOCRYPT-512 it was necessary to prune -Werror from the compiler flags before including the embedded C driver in the build. The same seems likely to be necessary for DFP when -Wall is added.