Delete UnknownAddress. It is a perfectly valid symbol value.

Delete UnknownAddress. It is a perfectly valid symbol value.

getSymbolValue now returns a value that in convenient for most callers:
* 0 for undefined
* symbol size for common symbols
* offset/address for symbols the rest

Code that needs something more specific can check getSymbolFlags.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241605 91177308-0d34-0410-b5e6-96231b3b80d8