[Bug bootstrap/116730] build is broken when building in subdirectory of a subdirectory of the src directory

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116730

--- Comment #41 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I still can't reproduce it even with a 14.2.0 worktree nested under the main
repo dir.

What does this show when run in the build dir?

grep -w VPATH x86_64-pc-linux-gnu/{.,32}/libstdc++-v3/src/libbacktrace/Makefile