[bpf] fix build and remove a compiler warning in Release mode

Patch by Brenden Blanco.

llvm-svn: 235814
diff --git a/llvm/lib/Target/BPF/InstPrinter/BPFInstPrinter.cpp b/llvm/lib/Target/BPF/InstPrinter/BPFInstPrinter.cpp
index 05f6d82..552288b 100644
--- a/llvm/lib/Target/BPF/InstPrinter/BPFInstPrinter.cpp
+++ b/llvm/lib/Target/BPF/InstPrinter/BPFInstPrinter.cpp
@@ -33,6 +33,7 @@
 }
 
 static void printExpr(const MCExpr *Expr, raw_ostream &O) {
+#ifndef NDEBUG
   const MCSymbolRefExpr *SRE;
 
   if (const MCBinaryExpr *BE = dyn_cast<MCBinaryExpr>(Expr))
@@ -44,6 +45,7 @@
   MCSymbolRefExpr::VariantKind Kind = SRE->getKind();
 
   assert(Kind == MCSymbolRefExpr::VK_None);
+#endif
   O << *Expr;
 }