Remove default argument from lambda to appease old MSVC.

llvm-svn: 282464
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index c6011cb..bca711f 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -2879,7 +2879,7 @@
   // in lexical order (this complexity is, sadly, required by C++17).
   llvm::Value *IdxPre =
       (E->getLHS() == E->getIdx()) ? EmitScalarExpr(E->getIdx()) : nullptr;
-  auto EmitIdxAfterBase = [&, IdxPre](bool Promote = true) -> llvm::Value * {
+  auto EmitIdxAfterBase = [&, IdxPre](bool Promote) -> llvm::Value * {
     auto *Idx = IdxPre;
     if (E->getLHS() != E->getIdx()) {
       assert(E->getRHS() == E->getIdx() && "index was neither LHS nor RHS");