IR: move the declaration of `VerifyDomInfo` (NFC)

[compnerd]

Summary

This moves the declaration of VerifyDomInfo into
llvm/IR/Dominators.h from llvm/Support/Debug.h. Although this is a
debugging utility, the definition of the symbol is in LLVMIR, not in
LLVMSupport. This moves the declaration to the containing modules'
header.

[rnk]

lgtm

[mehdi_amini]

Makes sense to me to align headers and libraries!

llvm/include/llvm/IR/Dominators.h

public:
   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
 };
 
 /// Verifier pass for the \c DominatorTree.
 struct DominatorTreeVerifierPass : PassInfoMixin<DominatorTreeVerifierPass> {
   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
 };
 
+/// Enables verification of dominator trees.
+///
+/// This check is expensive and is disabled by default.  `-verify-dom-info`
+/// allows selectively enabling the check without needing to recompile.
+extern bool VerifyDomInfo;
+
 /// Legacy analysis pass which computes a \c DominatorTree.
 class DominatorTreeWrapperPass : public FunctionPass {
   DominatorTree DT;
 
 public:
   static char ID;
 
   DominatorTreeWrapperPass();

llvm/include/llvm/Support/Debug.h

 
 /// \name Verification flags.
 ///
 /// These flags turns on/off that are expensive and are turned off by default,
 /// unless macro EXPENSIVE_CHECKS is defined. The flags allow selectively
 /// turning the checks on without need to recompile.
 /// \{
 
-/// Enables verification of dominator trees.
-///
-extern bool VerifyDomInfo;
-
 /// Enables verification of loop info.
 ///
 extern bool VerifyLoopInfo;
 
 /// Enables verification of MemorySSA.
 ///
 extern bool VerifyMemorySSA;