alley: Debugging options for running program under 'gdb' or 'valgrind' (static path)

[dtzWill]

Overview

alley runs allexes transparently, which is great but can make debugging failures a big difficult.
It might be useful to add simple flags that tell alley to use the given execution wrapper when invoking a static binary,
to enable testing the code with gdb or valgrind.

While this does expose the cache path, for debugging purposes I think this is okay (and anything that breaks as a result is the developer's responsibility).

What about on the JIT Path?

JIT path gdb should already work, kind-of maybe. valgrind might not like musl-based software by default, not sure.