yeah, i've been surprised how far i was able to get from an oss CPython tree and pre-built clang 7 binary installation.  If you have headers installed for common libraries like libssl-dev and libreadline-dev you can't produce an interpreter that'll work as those both lead to quick crashes.  also, in my experience optimized builds tend to be more problematic (too early to say if what i'm seeing are actual problems).

also, make sure llvm-symbolize (no suffixes) is in your path for it to auto-symbolize the traces showing you where in the code it pointed out issues.  when it points within shared libraries instead of the Python source tree - that's a hint that the library probably may need msan compilation.

I'm plodding through things to see if I can get a _useful_ buildbot setup (i don't care of some extension modules can't be covered for now) out of all of this.