Including cxxabi.h caused build failures because our definition of __cxa_get_globals conflicted with the one in the header (despite being in a different namespace -- apparently becaues of `extern "C"` the compiler considers them to be conflicting). Annoyingly, __cxa_get_globals is only defined by GNU's cxxabi.h and not LLVM's. But LLVM has a nicer __cxa_uncaught_exceptions() that we can perhaps use.

Also in C++17 there is a standard function we can call instead.