[llvm] Add symbol version support to llvm-ifs (PR #163030)

[via llvm-commits]

ur4t wrote:

>> GNU ld.bfd encounters some issues with generated glibc stub.

> The same version string appears in both version definitions and version requirements, which is a corner case I haven't taken into account.

It comes to me that the same version string might appear in multiple files, which is harder to be specified in IFS format, such as another field `VersionFrom` or something alike for items of `Symbols`.

Now I fully agree that we should focus on version definitions first. I will leave version requirements alone until necessary.

https://github.com/llvm/llvm-project/pull/163030