Pull in r320396 from upstream clang trunk (by Malcolm Parsons):

[Sema] Fix crash in unused-lambda-capture warning for VLAs

  Summary:
  Clang was crashing when diagnosing an unused-lambda-capture for a VLA
  because From.getVariable() is null for the capture of a VLA bound.
  Warning about the VLA bound capture is not helpful, so only warn for
  the VLA itself.

  Fixes: PR35555

  Reviewers: aaron.ballman, dim, rsmith

  Reviewed By: aaron.ballman, dim

  Subscribers: cfe-commits

  Differential Revision: https://reviews.llvm.org/D41016

This fixes a segfault when building recent audio/zynaddsubfx port
versions.

Reported by:	hps
MFC after:	3 days

contrib/llvm/tools/clang/include/clang/Sema/ScopeInfo.h

@@ -560,6 +560,7 @@ public:
     void markUsed(bool IsODRUse) { (IsODRUse ? ODRUsed : NonODRUsed) = true; }
 
     VarDecl *getVariable() const {
+      assert(isVariableCapture());
       return VarAndNestedAndThis.getPointer();
     }
     

contrib/llvm/tools/clang/lib/Sema/SemaLambda.cpp

@@ -1469,6 +1469,9 @@ void Sema::DiagnoseUnusedLambdaCapture(const LambdaScopeInfo::Capture &From) {
   if (CaptureHasSideEffects(From))
     return;
 
+  if (From.isVLATypeCapture())
+    return;
+
   auto diag = Diag(From.getLocation(), diag::warn_unused_lambda_capture);
   if (From.isThisCapture())
     diag << "'this'";