Avoid unused variable warnings on Linux

TBR=tsepez@chromium.org,dsinclair@chromium.org

Review URL: https://codereview.chromium.org/1949383002 .
diff --git a/xfa/fxfa/parser/xfa_object_imp.cpp b/xfa/fxfa/parser/xfa_object_imp.cpp
index 91497a5..dd5e1b4 100644
--- a/xfa/fxfa/parser/xfa_object_imp.cpp
+++ b/xfa/fxfa/parser/xfa_object_imp.cpp
@@ -4576,6 +4576,7 @@
   pNode->m_pParent = this;
   FX_BOOL ret = m_pDocument->RemovePurgeNode(pNode);
   ASSERT(ret);
+  (void)ret;  // Avoid unused variable warning.
 
   if (m_pChild == NULL || index == 0) {
     if (index > 0) {
@@ -4625,6 +4626,7 @@
   }
   FX_BOOL ret = m_pDocument->RemovePurgeNode(pNode);
   ASSERT(ret);
+  (void)ret;  // Avoid unused variable warning.
 
   int32_t nIndex = -1;
   pNode->m_pParent = this;