[scudo] Try to fix standalone build on armv7

When linking scudo standalone on armv7, it can't find symbols related to
unwinding (e.g. __aeabi_unwind_cpp_pr0). This is because it is passing
--unwindlib=none. This patch hacks around the issue by adding
COMPILER_RT_UNWINDER_LINK_LIBS to the link line.

I don't know anything about scudo, so I'm not sure what the original
intention was.

See also https://github.com/llvm/llvm-project/issues/56900

Differential Revision: https://reviews.llvm.org/D131250