Test clang with and without optimisations

[NWilson]

No description provided.

[NWilson]

The build failure here is due to #558

[carenas]

it might be better to implement this test as part of another job that might also test other things in parallel that aren''t currently covered.

for example as part of a windows build that uses the alternative clang compiler that comes with Visual Studio and that might be updated in the future to build for ARM64

[zherczeg]

Please update this patch to master.
After it is landed, the next step for me is #553

[NWilson]

Grr, there's still a build problem, even after your fix. I'll try and work it out as quick as possible.

It may be that running clang -fsanitize -O0 simply isn't sensible.

[carenas]

It may be that running clang -fsanitize -O0 simply isn't sensible

yes, whichs is why I suggested doing it on windows instead (without. the sanitize part, of course)

[NWilson]

@zherczeg I've fixed it; the next build should pass, and will be OK to merge.

[zherczeg]

Ok. Lets wait the CI then.