Silence "Undefined or garbage value returned to caller" static analysis warning. NFCI.

Author: RKSimon

clang/lib/Driver/Driver.cpp

@@ -3449,7 +3449,7 @@ class OffloadingActionBuilder final {
       return nullptr;
 
     // Let builders add host linking actions.
-    Action* HA;
+    Action* HA = nullptr;
     for (DeviceActionBuilder *SB : SpecializedBuilders) {
       if (!SB->isValid())
         continue;