Small self-contained example:

• clang https://godbolt.org/g/CJ6Pa7
• gcc https://godbolt.org/g/fIl2S5

nice, it hits the note

[ Note: This is intended to allow compiler transformations such as removal of empty loops, even when
termination cannot be proven. — end note ]

Yeah. I think we avoided the problem through the following mechanism:

1. Compiler optimized away MakeResponse(Route)
2. Calls that would've matched MakeResponse(Route) were instead redirected to MakeResponse(ManyRoutes) because it can cast Route->ManyRoutes

While this works, it's definitely a bit black-magicy, removing this weird function is 👍

Follow up from chat: AppVeyor build was 🍏 looks like a spurious error:
https://ci.appveyor.com/project/DennisOSRM/osrm-backend/build/1.0.8186

Also: after meging this into master Travis also had a spurious failure:
https://travis-ci.org/Project-OSRM/osrm-backend/jobs/233549233

where we were unable to download Clang, silently continued the build, used the system's pre-installed Clang 3.5 and then errored during compilation.

[Mason] Downloading package https://mason-binaries.s3.amazonaws.com/linux-x86_64/clang++/4.0.0.tar.gz...
CMake Error at cmake/mason.cmake:80 (message):
[Mason] Failed to download  https://mason-binaries.s3.amazonaws.com/linux-x86_64/clang++/4.0.0.tar.gz:
curl: (56) SSL read: error:00000000:lib(0):func(0):reason(0), errno 104