Dwarf Exception Handling now on FreeBSD!

[Walter Bright via Digitalmars-d]

32/64 support now on Linux and FreeBSD.

   https://github.com/D-Programming-Language/dmd/pull/5376

Turns out that FreeBSD is close enough to Linux that it "just worked".

Recently, there was a long thread entitled "C++17" where people are asking for 
better C++ interoperability. Well, here's a ripe plum for anyone wanting 
valuable compiler street cred!

Make the Dwarf EH support work on OSX 32 and 64.

I bet that nearly all the work will be in changing the ELF fixups to MACH-O 
fixups in the gcc_except_table and eh_frame sections. Use an object dumper to 
see what g++ uses for fixups in those sections, and do the same.

As for me, I'll be implementing C++ multiple inheritance class layout, because 
Manu's problems have made it clear we have to do that.