CodeGen: Stop using DIDescriptor::is*() and auto-casting

Same as r234255, but for lib/CodeGen and lib/Target.

llvm-svn: 234258
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
index 993d421..92c37c5 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
@@ -153,7 +153,7 @@
   }
 
   bool variableHasComplexAddress() const {
-    assert(Var.isVariable() && "Invalid complex DbgVariable!");
+    assert(Var && "Invalid complex DbgVariable!");
     assert(Expr.size() == 1 &&
            "variableHasComplexAddress() invoked on multi-FI variable");
     return Expr.back().getNumElements() > 0;