I have a brand-new Fedora Linux 32 computer based on AMD 3950X, with a minimal mozconfig file. Just a few days ago, I was patching bug 1626015, so I know it's not my system.

. $topsrcdir/browser/config/mozconfig

Options for client.mk.

mk_add_options MOZ_OBJDIR=@TOPSRCDIR@/../fx-debug

Options for 'configure' (same as command-line options).

ac_add_options --enable-debug
ac_add_options --disable-optimize

js/src> ERROR: Missing option in @old_configure_options in .../mozilla-central/build/moz.configure/old.configure: --enable-cpp-rtti

hg blame points to bug 1639815.

Yes, I re-ran mach bootstrap. No change.

I am curious, why do you need this option?

Building with D76288 backed out works just fine.

This bug might be a direct result of a botched Mercurial checkout, with the same error as bug 1604486. I have no idea why.

The only case where I'd expect this error to happen is if for some reason js/src/old-configure is newer than js/src/old-configure.in but not actually up-to-date wrt changes in js/src/old-configure.in, which is not supposed to happen.

Set release status flags based on info from the regressing bug 1639815

Oh, it happens because someone (like me) is trying to save some thirty minutes checking out mozilla-central. Sorry about that.