The debug-compile-with-warnings task compiles with -Werror using GCC 5.4. But Travis compiles with -Werror using clang. Many times I've had a passing evergreen patch build, push to master, then find out I broke the Travis build because clang produces different warnings.

Ideally, we should compile with -Werror everywhere. If that is not reasonable, we should at least build with -Werror using clang, so Evergreen fails on the same warnings that Travis does.