Make lldb -Werror clean for -Wstring-conversion

Also found/fixed one bug identified by this warning in
RenderScriptx86ABIFixups.cpp where a string literal was being used in an
effort to provide a name for an instruction/register, but was instead
being passed as the bool 'isVolatile' parameter.

llvm-svn: 291198
diff --git a/lldb/tools/lldb-perf/lib/Results.cpp b/lldb/tools/lldb-perf/lib/Results.cpp
index 17a022f..a4cdce5 100644
--- a/lldb/tools/lldb-perf/lib/Results.cpp
+++ b/lldb/tools/lldb-perf/lib/Results.cpp
@@ -76,8 +76,7 @@
   } break;
 
   default:
-    assert(!"unhandled result");
-    break;
+    llvm_unreachable("unhandled result");
   }
 }
 
@@ -125,8 +124,7 @@
                                result->GetAsUnsigned()->GetValue(), true);
   } break;
   default:
-    assert(!"unhandled result");
-    break;
+    llvm_unreachable("unhandled result");
   }
 }
 void Results::Write(const char *out_path) {