Building Emacs with 'make bootstrap' on my msys2 WIN10 system works fine
up to this commit.

Reverting this merge commit

 git revert -m 1 38179f85f8f7236d5de8d9a4333b6a1d4ded63f0

Seems to fix it.

Very minor gdb debugging points to gccjit being in Vlibrary_cache
even before the first call to load_gccjit_if_necessary,
which wouldn't seem to make sense, but I don't know.

The error output is attached.

João