[llvm] [ThinLTO] Don't mark calloc function dead (PR #72673)

[Steven Wu via llvm-commits]

cachemeifyoucan wrote:

> The problem arises only when two (or more) libcalls are folded into one (or more) other libcalls. 

The problem here is all allocation functions are not in the RuntimeLibcalls list. All RuntimeLibcalls functions are preserved by LTO process (in general, unless for specific platform they are not available) because they can be produced by backend even if the bitcode object file don't reference them. There is no difference from this case, which `calloc` doesn't get referenced before optimization.

https://github.com/llvm/llvm-project/pull/72673