test: fix fiber stack overflow test not overflowing

test/unit/guard.cc calls stack_break_f() recursively until the stack
overflows and a signal is fired, however it relies on undefined behavior
when compares pointers to local variables. Fixed by comparing
__builtin_frame_address() instead.

One of the examples of this UB is when ASAN allocates local variables on
fake stacks, in that case the test completes without the stack overflow.

Also this patch disables ASAN for stack_break_f() to keep the array on the
fiber stack (see the corresponding comment) and marks it as volatile to
avoid optimizing it away by the compiler.

Closes tarantool/tarantool-qa#323

NO_DOC=test fix
NO_CHANGELOG=test fix