When looking for symbols, find load addresses in a more robust way.
When looking for symbols, find load addresses in a more robust way.

IRExecutionUnit previously replicated a bunch of logic that already
existed elsewhere for the purpose of getting a load address for a
symbol.  This approach failed to resolve certain types of symbols.
Instead, we now use functions on SymbolContext to do the address
resolution.

This is a cleanup of IRExecutionUnit::FindInSymbols, and also fixes a
latent bug where we looked at the wrong SymbolContext to determine
whether or not it is external.

<rdar://problem/24770829>


git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@261704 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb