It was recently reported in WT-5567 that some compilation warning-turned-to errors were not picked up by the Evergreen pull request testing, specifically, the 2 compilers tasks compile-gcc and compile_clang. 

The default configure setting CFLAGS="-ggdb -fPIC" in Evergreen seems to be the factor that made the difference. If we skip the "-ggdb" CFLAGS setting, those -Werrors would be captured, otherwise not. We should revisit the -ggdb setting for those compilers tasks to avoid missing capture of compilation warnings.