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

[schwab--- via Gcc-bugs]

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

--- Comment #17 from Andreas Schwab <sch...@linux-m68k.org> ---
No, top_builddir is wrong.  The rule wants to link to a file in the _source_
directory.