Add thread tracking extension to myst-gdb

[asvrada]

This extension tracks all threads created inside Enclave, and report their pid, tid to facilitate debugging.
This extension also tracks all command-line arguments that a process runs.

Example usage: tests/dotnet-lib-5

make gdb-runner

>>> myst-thread

        myst-thread: Mystikos thread tracker
        Commands:
        myst-thread help
          Print this message

        myst-thread thread
          List all tracked threads
        
        myst-thread cmdline
          List the command line for each process
        
        myst-thread exe
          List the executable for each process

        myst-thread cwd
          List the current working directory for each process
        
>>> myst-thread thread
List of Mystikos controlled threads:
ppid pid tid(target_tid)
100 101 101(5666)
100 101 102(5730)
100 101 103(5731)
100 101 104(5732)
100 101 105(5733)
100 101 106(5734)
100 101 107(5736)
100 101 108(5738)
100 101 109(5742)
100 101 110(5746)
100 101 111(5747)
100 101 112(5748)
100 101 113(5749)
100 101 114(5750)
100 101 117(5766)
100 101 118(5767)
100 101 119(5771)
100 101 120(5772)
100 101 121(5774)
100 101 122(5775)
>>> myst-thread cmdline
Process 101 (Parent 100) cmdline: /runner/bin/Release/net5.0/runner /testcases/pass.1 /dotnet-lib-release/

[vtikoo]

Thanks for adding this, looks good!

[anakrish]

We also need to make sure that the hook functions are compiled with debug information, and aren't optimized out.

Do we expect the debugger extension to work in a RelWithDebInfo build of Mystikos?