SIL: force the destructor of DeadEndBlocks to be placed in a C++ file

Otherwise it can happen that it is generated in a SwiftCompilerSources module and that results in unresolved-symbols linker errors.

Author: eeckstein

include/swift/SIL/BasicBlockUtils.h

@@ -73,6 +73,8 @@ class DeadEndBlocks {
 public:
   DeadEndBlocks(const SILFunction *f) : f(f) {}
 
+  ~DeadEndBlocks();
+
   /// Returns true if \p BB is a dead-end block.
   bool isDeadEnd(const SILBasicBlock *block) {
     if (!didComputeValue) {

lib/SIL/Utils/BasicBlockUtils.cpp

@@ -369,6 +369,11 @@ void swift::mergeBasicBlockWithSingleSuccessor(SILBasicBlock *BB,
 //                              DeadEndBlocks
 //===----------------------------------------------------------------------===//
 
+// Force the compiler to generate the destructor in this C++ file.
+// Otherwise it can happen that it is generated in a SwiftCompilerSources module
+// and that results in unresolved-symbols linker errors.
+DeadEndBlocks::~DeadEndBlocks() {}
+
 // Propagate the reachability up the control flow graph.
 void DeadEndBlocks::propagateNewlyReachableBlocks(unsigned startIdx) {
   for (unsigned idx = startIdx; idx < reachableBlocks.size(); ++idx) {