Re-enable -Wall on Unix

[jmarrec]

Issue overview

8db1b93 had disabled -Werror AND -Wall

#3577 only re-enabled -Werror but not -Wall

Possible Solution

Re-enable -Wall, and fix all build errors that will arise in the process.

Details

Environment

Some additional details about your environment for this issue (if relevant):

• Platform (Operating system, version): Ubuntu 18.04
• Version of OpenStudio (if using an intermediate build, include SHA): develop (post 3.0.1) c68fcf6

Context

-Wall is needed. I just got hit with a problem today, where I forgot a return <object> in a method that wasn't void. -Wall, which enables -Wreturn-type, would have caught this problem, and that's when I realized it wasn't turned on.