Add a way to load an image using a library name and list of paths.

This provides an efficient (at least on Posix platforms) way to offload to the
target process the search & loading of a library when all we have are the 
library name and a set of potential candidate locations.

<rdar://problem/40905971>

llvm-svn: 335912
diff --git a/lldb/source/Expression/FunctionCaller.cpp b/lldb/source/Expression/FunctionCaller.cpp
index 622d801..9742ed0 100644
--- a/lldb/source/Expression/FunctionCaller.cpp
+++ b/lldb/source/Expression/FunctionCaller.cpp
@@ -91,8 +91,12 @@
       m_jit_start_addr, m_jit_end_addr, m_execution_unit_sp, exe_ctx,
       can_interpret, eExecutionPolicyAlways));
 
-  if (!jit_error.Success())
+  if (!jit_error.Success()) {
+    diagnostic_manager.Printf(eDiagnosticSeverityError,
+                              "Error in PrepareForExecution: %s.",
+                              jit_error.AsCString());
     return false;
+  }
 
   if (m_parser->GetGenerateDebugInfo()) {
     lldb::ModuleSP jit_module_sp(m_execution_unit_sp->GetJITModule());