QNX provides cxxabi.h from LLVM libc++abi, which does not declare
__cxa_get_globals but provides its implementation in the library.
To make things more fun, QNX developers commented _LIBCPPABI_VERSION
definition, which breaks detection of libc++abi in uncaught_exceptions.hpp.
There is also cxxabi.h from glibcxx that does provide __cxa_get_globals
declaration. We want to use that declaration, if possible, to avoid possible
mismatch in attributes.
This commit adds non-glibcxx cxxabi.h on QNX to the list of platforms that
need our declaration of __cxa_get_globals.
Fixes https://github.com/boostorg/core/issues/59.
420dff80b5