Add option to treat warnings as errors (backport #2676) (#2677)

* Add option to treat warnings as errors (#2676)

Add --warnings-as-errors option

(cherry picked from commit 49894666

)

# Conflicts:
#	core/src/main/scala/chisel3/experimental/hierarchy/Definition.scala
#	core/src/main/scala/chisel3/internal/Builder.scala
#	src/main/scala/chisel3/aop/injecting/InjectingAspect.scala
#	src/main/scala/chisel3/stage/ChiselOptions.scala
#	src/main/scala/chisel3/stage/package.scala
#	src/main/scala/chisel3/stage/phases/Elaborate.scala

* Resolve backport conflicts

Co-authored-by: Zachary Yedidia <zyedidia@gmail.com>
Co-authored-by: Jack Koenig <koenig@sifive.com>