[DebugInfoMetadata] Refactor DIExpression::prepend constants (NFC)

Refactor DIExpression::With* into a flag enum in order to be less
error-prone to use (as discussed on D60866).

Patch by Djordje Todorovic.

Differential Revision: https://reviews.llvm.org/D61943

llvm-svn: 361137
diff --git a/llvm/lib/Transforms/IPO/GlobalOpt.cpp b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
index ca0e580..c4fb3ce 100644
--- a/llvm/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
@@ -1671,7 +1671,8 @@
             dwarf::DW_OP_constu, ValMinus,
             dwarf::DW_OP_mul, dwarf::DW_OP_constu, ValInit,
             dwarf::DW_OP_plus};
-        E = DIExpression::prependOpcodes(E, Ops, DIExpression::WithStackValue);
+        bool WithStackValue = true;
+        E = DIExpression::prependOpcodes(E, Ops, WithStackValue);
         DIGlobalVariableExpression *DGVE =
           DIGlobalVariableExpression::get(NewGV->getContext(), DGV, E);
         NewGV->addDebugInfo(DGVE);