[llvm] [Support] Recognise the '+' char for positive integers (PR #135856)

[Ebuka Ezike via llvm-commits]

da-viper wrote:

It will only be more permissive if the `+` at the start of a stringRef signifies something else.

I did check the callers of the `StringRef::getAsInteger` function, this is not the case. 

The only new change was in the `llvm-symbolizer` to handle when the address starts with a `+` to match `addr2line`

https://github.com/llvm/llvm-project/pull/135856