Fix bug with function resolution when using IR Interpreter

Summary: Recent changes to the expression parser broke function name resolution when using the IR interpreter instead of JIT. This patch changes the IRMemoryMap ivar in InterpreterStackFrame to an IRExecutionUnitSP (which is a subclass), allowing InterpreterStackFrame::ResolveConstantValue() to call FindSymbol() on the name of the Value when it's a FunctionVal. It also changes IRExecutionUnit::FindInSymbols() to call GetFileAddress() on the symball if ResolveCallableAddress() fails and there is no valid Process.

Reviewers: spyffe

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D17745

llvm-svn: 262407