Handle mergiraf crashes

[xmo-odoo]

Issue occurred trying to forward-port odoo/odoo#229795 onto 19.0, specifically commit 430ee4506797413bef8837b3538f6dbd64e1c353 onto 19.0 (~99f8190e11bfff38eaaee569ed895484bfce7589)

This causes a few conflicts:

Auto-merging addons/mail/static/tests/emoji/emoji.test.js
CONFLICT (content): Merge conflict in addons/mail/static/tests/emoji/emoji.test.js
Auto-merging addons/web/static/src/core/emoji_picker/emoji_data.js
CONFLICT (content): Merge conflict in addons/web/static/src/core/emoji_picker/emoji_data.js
error: could not apply 430ee4506797... [FIX] web: emoji picker crash for non-English

but nothing out of the ordinary... until mergiraf gets involved

git -C odoo -c merge.conflictStyle=diff3 -c merge.mergiraf.name=mergiraf -c merge.mergiraf.driver="mergiraf merge --git %O %A %B -s %S -x %X -y %Y -p %P -l %L" -c core.attributesfile=/home/xmo-odoo/odoo/nightly/attrfile merge-tree --merge-base 430ee4506797413bef8837b3538f6dbd64e1c353~1 99f8190e11bfff38eaaee569ed895484bfce7589 430ee4506797413bef8837b3538f6dbd64e1c353

thread '<unknown>' has overflowed its stack
fatal runtime error: stack overflow, aborting
Aborted (core dumped)
fatal: failure to merge

mergiraf disabled for now.

[xmo-odoo]

INFO: git merge has the returncode 1 on a normal merge failure, but when the merge driver blows up it seems to have the returncode 128, with "fatal: failure to merge" on stderr. stderr may need to come into play as the existing code already checks the error code 128 for "inflateInit" errors.

On stack overflow I get a returncode 134, this is SIGABRT rather than the expected SIGSEGV or SIGBUS because the rust rt catches the stack overflow and runs rtabort!: https://github.com/rust-lang/rust/blob/235a4c083eb2a2bfe8779d211c3232f39396de00/library/std/src/sys/pal/unix/stack_overflow.rs#L101-L127

So this can be tested by juggling the PATH and creating a fake mergiraf which calls exit(128 + SIGABRT).