- `__cxa_*` runtime functions are expected to be in the `abi` namespace,
which is currently an alias for `__cxxabiv1`.
- Rely on the header provided by `libcxxabi` for functions that we do
not implement ourselves anymore.
This will help C++ code that uses exceptions to be tinier. For example,
this change shaves away 1000 lines of assembly code from LLVM's libcxx,
which is 0.7% of all assembly instructions in the entire library.
We now have an `#include <cxxabi.h>` header which defines all the APIs
Cosmopolitan's implemented so far. The `cosmocc` README.md file is now
greatly expanded with documentation.
