[sancov] Introduce optional callback for stack-depth tracking (#138323)

Normally -fsanitize-coverage=stack-depth inserts inline arithmetic to
update thread_local __sancov_lowest_stack. To support stack depth
tracking in the Linux kernel, which does not implement traditional
thread_local storage, provide the option to call a function instead.

This matches the existing "stackleak" implementation that is supported
in Linux via a GCC plugin. To make this coverage more performant, a
minimum estimated stack depth can be chosen to enable the callback mode,
skipping instrumentation of functions with smaller stacks.

With -fsanitize-coverage-stack-depth-callback-min set greater than 0,
the __sanitize_cov_stack_depth() callback will be injected when the
estimated stack depth is greater than or equal to the given minimum.

0 files changed, 0 insertions, 0 deletions