I was looking at the libcxx buildbots that we're maintaining at Linaro
 and I noticed that they all default to building in Debug mode. I
think we should either
(a) Switch to Release (or RelWithDebInfo), or
(b) Specify CMAKE_BUILD_TYPE explicitly as Debug so it serves as
documentation in zorg.
What is the community's preference? Is there a reason to stick with
Debug mode for the buildbots? Note that this only affects 6 builders
(aarch64, armv8 and armv7 with/without exceptions), although I don't
mind touching other bots in zorg if need be.
 http://llvm.validation.linaro.org/ section "Library bots"