This is safer for signal handlers.

MinGW 7.2 (x86_64) build failed

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.

This should prevent stack traces from spurriously pointing at the line after the one where the call actually happened.

On Linux this cuts 56% off the run time of the fuzz test (aka 2.28x speedup).

On Windows this makes it practical to run the fuzz test at all -- previously it was wayyyyyyy too slow.

The calling convention must go inside the parentheses when declaring a
function pointer.

WINBOOL is apparently a MinGW-ism.

Fix as done elsewhere so that it builds correctly on Musl libc
as well as Glibc.
Signed-off-by: Justin Cormack <justin@specialbusservice.com>

Fixes a spurrious test failure with out-of-tree builds.

Fixes #235
Closes #325

The MSVC runtime was heavily refactored, so the internal function we call to
get the current exception count changed for newer MSVC versions (as did the
offset).

This avoids an unused function warning for crashHandler.

- Reduce noise.
- Trace through async callbacks.

A compatibility layer is provided to ease migration.

Distinguishing between "local bugs" and "preconditions" was proving difficult in practice, because a precondition failure in one function may very well indicate a bug in a calling function, but the exception may be thrown through that function, thus when caught the classification is nonsensical. The distinction also was not as useful as imagined. So, I eliminated this distinction.

Thanks to Bryan Boreham <bjboreham@gmail.com> for much help getting this started.

atos(1) doesn't actually have a '-d' flag, but its inclusion was
innocuous (and suppressed a warning) until OS X 10.10.