remove segfault when (t)emacs starts up

emacs is currently failing to build on my alpine box (both from a git checkout of the emacs repo as well as via abuild). In particular, the bootstrap src/temacs executable which loads elisp code to produce src/emacs was segfaulting within the backtrace() method from libexecinfo. I found this merge request which clarifies that libexecinfo has apparently never worked: !36722 (closed). That merge request advises packages to simply patch it out, so that's what this change does.

However, it's also very important to note that before quite recently, this build wasn't failing! I'm sure of this because I know that my spack pull request at https://github.com/spack/spack/pull/29088 which builds emacs from source was working on my alpine box a while ago without this change! I am assuming this is due to the removal of libexecinfo from aports, but I'm not sure. cc @psykose: I don't understand why removing the package from aports would change this behavior whatsoever, but this may imply that 50795a14 could also cause other packages to segfault where they weren't previously, although this behavior may not be observed at all since emacs may be the only one to call backtrace() within its build script. This is likely not going to cause any problems, but if a package e.g. calls backtrace() and then does some other cleanup, and that package also segfaults now where it didn't before, I could see that potentially causing breakage.