[boost] [exception] exception_ptr for GCC

Hi, My quest for a general exception_ptr for GCC has reached its end, in the sense of, "I can't make it any better without modifying GCC." My current code is extremely fragile regarding code generation (it depends on the layout of the functions in the file) and there is one circumstance under which it leaks the exception object, but in general it works quite well. The header file, source file, and a file containing test cases are attached. Even though this can obviously not be used in production code, it's an interesting study of absurd things you can do in order to get around the limitations of a fixed ABI. Sebastian