mac build: maybe fix reproducibility fail (_cbor.cpython-39-darwin.so)

vagrants-iMac:electrum vagrant$ ./contrib/osx/compare_dmg dist/electrum-4.3.0-ghost43.dmg /Users/vagrant/Desktop/electrum-4.3.0-thomas1.dmg
[...]
Extracting signatures from release app...
Created mac_extracted_sigs.tar.gz
Applying extracted signatures to unsigned app...
Done. .app with sigs applied is at: /tmp/electrum_compare_dmg/signed_app
++ diff -qr /tmp/electrum_compare_dmg/signed_app /tmp/electrum_compare_dmg/dmg2
+ diff='Files /tmp/electrum_compare_dmg/signed_app/Electrum.app/Contents/MacOS/cbor/_cbor.cpython-39-darwin.so and /tmp/electrum_compare_dmg/dmg2/Electrum.app/Contents/MacOS/cbor/_cbor.cpython-39-darwin.so differ'
+ diff='diff errored'
+ set +x
diff errored
DMGs do *not* match.
failure

user@user-VirtualBox:~/wspace/tmp$ vbindiff comp/signed_app/_cbor.cpython-39-darwin.so comp/dmg2/_cbor.cpython-39-darwin.so

comp/signed_app/_cbor.cpython-39-darwin.so
0000 6AC0: 00 5F 50 79 49 6E 69 74  5F 5F 63 62 6F 72 2E 6D  ._PyInit __cbor.m
0000 6AD0: 6F 64 65 66 00 5F 43 62  6F 72 4D 65 74 68 6F 64  odef._Cb orMethod
0000 6AE0: 73 00 2F 70 72 69 76 61  74 65 2F 76 61 72 2F 66  s./priva te/var/f
0000 6AF0: 6F 6C 64 65 72 73 2F 35  36 2F 64 38 36 70 35 39  olders/5 6/d86p59
0000 6B00: 37 31 31 67 7A 63 62 38  73 31 71 37 31 36 78 31  711gzcb8 s1q716x1
0000 6B10: 6C 63 30 30 30 30 67 6E  2F 54 2F 70 69 70 2D 69  lc0000gn /T/pip-i
0000 6B20: 6E 73 74 61 6C 6C 2D 36  6D 69 36 68 6C 75 65 2F  nstall-6 mi6hlue/
comp/dmg2/_cbor.cpython-39-darwin.so
0000 6AC0: 00 5F 50 79 49 6E 69 74  5F 5F 63 62 6F 72 2E 6D  ._PyInit __cbor.m
0000 6AD0: 6F 64 65 66 00 5F 43 62  6F 72 4D 65 74 68 6F 64  odef._Cb orMethod
0000 6AE0: 73 00 2F 70 72 69 76 61  74 65 2F 76 61 72 2F 66  s./priva te/var/f
0000 6AF0: 6F 6C 64 65 72 73 2F 37  68 2F 70 33 30 7A 5F 74  olders/7 h/p30z_t
0000 6B00: 79 31 35 30 31 32 70 66  5F 33 64 79 78 62 73 39  y15012pf _3dyxbs9
0000 6B10: 33 34 30 30 30 30 67 6E  2F 54 2F 70 69 70 2D 69  340000gn /T/pip-i
0000 6B20: 6E 73 74 61 6C 6C 2D 30  68 64 39 63 35 6D 65 2F  nstall-0 hd9c5me/

related: pypa/pip#6505

contrib/osx/make_osx

@@ -92,6 +92,10 @@ rm -rf "$VENV_DIR"
 python3 -m venv $VENV_DIR
 source $VENV_DIR/bin/activate
 
+# don't add debug info to compiled C files (e.g. when pip calls setuptools/wheel calls gcc)
+# see https://github.com/pypa/pip/issues/6505#issuecomment-526613584
+export CFLAGS="-g0"
+
 info "Installing build dependencies"
 python3 -m pip install --no-build-isolation --no-dependencies --no-warn-script-location \
     -Ir ./contrib/deterministic-build/requirements-build-base.txt \