[libunwind] [libunwind][AIX] Remove weak declaration "__xlcxx_personality_v0" (PR #112436)

[Xing Xue via cfe-commits]

xingxue-ibm wrote:

> I think a small test case could be added with a `int main(void) {}` C program linked with -`brtl` and `LDR_PRELOAD`/`LDR_PRELOAD64` set to `libunwind.a(libunwind.so.1)`.

Added a test case `aix_runtime_link.pass.cpp` although the test case needs to be in C. The reason for the `.cpp` suffix is the libunwind test configuration does not recognize `.c` as a suffix for test cases. Also, `%{cxx}` is used to compile. However, the test configuration uses `-nostdlib++ -L %{lib} -lunwind -ldl -Wl,-bbigtoc` as link flags so it does not link with `libc++abi` and the test case does fail without the change.

https://github.com/llvm/llvm-project/pull/112436