Auto merge of #141375 - kraj:kraj/aarch64-musl, r=Mark-Simulacrum

Disable libunwind cross-architecture unwinding

Building with _LIBUNWIND_IS_NATIVE_ONLY disables code for cross-architecture unwinding It also enables some additional code that handles PAC-specific unwind info it helps compiling with the -mbranch-protection=pac or -mbranch-protection=standard flags

This fixes build with clang/musl on aarch64

Author: bors