[lldb/Target] Refine source display warning for artificial locations (NFC)

[mib]

Summary

This is a post-review update for D115313, to rephrase source display
warning messages for artificial locations, making them more
understandable for the end-user.

[aprantl]

Thanks, I think this is much easier to understand!

lldb/source/Target/StackFrame.cpp

if (target) {
                   source_lines_before, source_lines_after, "->", &strm);
           if (num_lines != 0)
             have_source = true;
           // TODO: Give here a one time warning if source file is missing.
           if (!m_sc.line_entry.line) {
             ConstString fn_name = m_sc.GetFunctionName();
 
             if (!fn_name.IsEmpty())
-              strm.Printf("Warning: the current PC is an artificial location "
-                          "in function %s.",
-                          fn_name.AsCString());
+              strm.Printf(
+                  "Note: this address is compiler-generated code in function "
+                  "%s that has no source code associated with it.",
             else
-              strm.Printf(
-                  "Warning: the current PC is an artificial location "
-                  "but lldb couldn't associate it with a function in %s.",
-                  m_sc.line_entry.file.GetFilename().GetCString());
+              strm.Printf("Note: this address is compiler-generated code that "
+                          "has no source code associated with it.");
             strm.EOL();
           }
         }
       }
       switch (disasm_display) {
       case Debugger::eStopDisassemblyTypeNever:
         break;
 

lldb/test/API/source-manager/TestSourceManager.py

def test_artificial_source_location(self):
         self.build(dictionary=d)
 
         lldbutil.run_to_source_breakpoint(
             self, 'main',
             lldb.SBFileSpec(src_file, False))
 
         self.expect("run", RUN_SUCCEEDED,
                     substrs=['stop reason = breakpoint', '%s:%d' % (src_file,0),
-                             'Warning: the current PC is an artificial ',
-                             'location in function '
-                             ])
+                             'Note: this address is compiler-generated code in '
+                             'function', 'that has no source code associated '
+                             'with it.'])