No need to include this possibly non-existing file when using our own backtrace() implementation, it's only needed for the libc-provided one. Because of this it's currently not possible to build musl with backtrace enabled. (cherry picked from commit 1c4776dbc3e7d0a73bd62bae78d509c3c54045d6) Signed-off-by: Willy Tarreau <w@1wt.eu>