Revert libunwind change to fix backtrace segfault on aarch64
Revert commit 22b615a96593 from llvm git (by Daniel Kiss):
[libunwind] Support for leaf function unwinding. Unwinding leaf function is useful in cases when the backtrace finds a leaf function for example when it caused a signal. This patch also add the support for the DW_CFA_undefined because it marks the end of the frames. Ryan Prichard provided code for the tests. Reviewed By: #libunwind, mstorsjo Differential Revision: https://reviews.llvm.org/D83573 Reland with limit the test to the x86_64-linux target.
Bisection has shown that this particular upstream commit causes programs
using backtrace(3) on aarch64 to segfault. This affects the lang/rust
port, for instance. Until we can upstream to fix this problem, revert
the commit for now.
Reported by: mikael
PR: 256864