Enable cross-directory ccache

[lockshaw]

Description of changes:

The current ccache setup is very limited in its ability to cache between directories due to the fact that the compiler-generated debug info and any __FILE__ macros cause builds to differ between directories, which is quite annoying if you are using ff-dev and would like to quickly ffpr down a PR and build it as you end up building from scratch. This PR adds the necessary compiler flags to make debug info and __FILE__ macros use relative paths, and then adds a wrapper around gdb that ensures that the debugging experience isn't affected (the only limitation is that you have to be running the debugger inside the nix environment, which you essentially have to do anyway).

Related Issues:

Linked Issues:

• Issue #

Issues closed by this PR:

• Closes #

---

This change is 

[Marsella8]

From my very limited understanding of nix, everything seems good.

Reviewed 7 of 8 files at r1, all commit messages.
Reviewable status: 7 of 8 files reviewed, 2 unresolved discussions (waiting on @lockshaw and @reyna-abhyankar)

---

.flake/pkgs/ffdb/default.nix line 32 at r1 (raw file):

        python3
      ]}
    cp $out/bin/gdb $out/bin/ffdb

so this effectively auto-executes ffdb.py before every gdb call right?

---

.flake/pkgs/ffdb/ffdb.py line 9 at r1 (raw file):

gdb.execute('set history save on')

# python

The commented out code should either be deleted or updated? (e.g. MachineViewPrinter still refers to the old interface).

[lockshaw]

Reviewable status: 6 of 8 files reviewed, 2 unresolved discussions (waiting on @Marsella8 and @reyna-abhyankar)

---

.flake/pkgs/ffdb/default.nix line 32 at r1 (raw file):

Previously, Marsella8 wrote…

so this effectively auto-executes ffdb.py before every gdb call right?

Correct

---

.flake/pkgs/ffdb/ffdb.py line 9 at r1 (raw file):

Previously, Marsella8 wrote…

The commented out code should either be deleted or updated? (e.g. MachineViewPrinter still refers to the old interface).

Done.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (master@030bfd6). Learn more about missing BASE report.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1539   +/-   ##
=========================================
  Coverage          ?   78.50%           
=========================================
  Files             ?      867           
  Lines             ?    28904           
  Branches          ?      778           
=========================================
  Hits              ?    22690           
  Misses            ?     6214           
  Partials          ?        0           

Flag	Coverage Δ
unittests	78.50% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.