Fix a nondeterminism in the debug info for VLA size expressions.

The artificial variable describing the array size is supposed to be
called "__vla_expr", but this was implemented by retrieving the name
of the associated alloca, which isn't a reliable source for the name,
since nonassert compilers may drop names from LLVM IR.

rdar://problem/45924808

llvm-svn: 346542
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index f6b7629..9f09119 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -1197,6 +1197,8 @@
 
 private:
   CGDebugInfo *DebugInfo;
+  /// Used to create unique names for artificial VLA size debug info variables.
+  unsigned VLAExprCounter = 0;
   bool DisableDebugInfo = false;
 
   /// DidCallStackSave - Whether llvm.stacksave has been called. Used to avoid