Our cql parser uses large amounts of stack, and can overflow it
in debug mode with clang. To prevent this stack overflow,
temporarily use a larger (1MB) stack.
We can't use seastar::thread(), since do_with_cql_parser() does
not yield. We can't use std::thread(), since lw_shared_ptr()'s
debug mode will scream murder at an lw_shared_ptr used across
threads (even though it's perfectly safe in this case). We
can't use boost::context2 since that requires the library to
be compiled with address sanitizer support, which it isn't on
Fedora. So we use a fiber switch using the getcontext() function
familty. This requires extra annotations for debu mode, which are
added.
cb6231d1e2