Implement a demangleable strong ownership symbol mangling.
* The original module symbol mangling scheme turned out to be
undemangleable.
* The hoped-for C++17 compatibility of weak ownership turns out to be
fragile
* C++20 now has better ways of controlling C++17 compatibility
The issue is captured on the ABI list at:
https://github.com/itanium-cxx-abi/cxx-abi/issues/134
GCC implements this new mangling.
The old mangling is unceremoniously dropped. No backwards
compatibility, no deprectated old-mangling flag. It was always
labelled experimental. (Old and new manglings cannot be confused.)
Reviewed By: dblaikie
Differential Revision: https://reviews.llvm.org/D122256
ae4dce8659