llvm: libomptarget support (#14060)

This allows the llvm build to support:

* clang cuda
* libomptarget for:
  * current host
  * cuda
* bitcode compilation of libomptarget device runtime for inlining by 
  bootstrapping libomptarget
* split dwarf information support as an option for debug builds, if you need a
  debug build, for the love of all that's good in the universe use this flag
* adds necessary dependencies for shared library builds and libomp and
  libomp target to build correctly
* new version of z3 to make it sufficient to build recent llvm

The actual change is much smaller than the diff, this is because it's been formatted with black.  I realize this kinda sucks right now, but I'm hoping it will make future updates here less painful.