[Analysis] Fix gcc warnings about unused variables [NFC]

gcc warned with:
 [236/4788] Building CXX object lib/Analysis/CMakeFiles/LLVMAnalysis.dir/LazyValueInfo.cpp.o
 ../lib/Analysis/LazyValueInfo.cpp: In member function 'void llvm::LazyValueInfo::forgetValue(llvm::Value*)':
 ../lib/Analysis/LazyValueInfo.cpp:1978:13: warning: unused variable 'Impl' [-Wunused-variable]
  1978 |   if (auto *Impl = getImpl())
       |             ^~~~
 ../lib/Analysis/LazyValueInfo.cpp: In member function 'void llvm::LazyValueInfo::eraseBlock(llvm::BasicBlock*)':
 ../lib/Analysis/LazyValueInfo.cpp:1983:13: warning: unused variable 'Impl' [-Wunused-variable]
  1983 |   if (auto *Impl = getImpl())
       |             ^~~~
 ../lib/Analysis/LazyValueInfo.cpp: In member function 'void llvm::LazyValueInfo::clear()':
 ../lib/Analysis/LazyValueInfo.cpp:1988:13: warning: unused variable 'Impl' [-Wunused-variable]
  1988 |   if (auto *Impl = getImpl())
       |             ^~~~
 ../lib/Analysis/LazyValueInfo.cpp: In member function 'void llvm::LazyValueInfo::printLVI(llvm::Function&, llvm::DominatorTree&, llvm::raw_ostream&)':
 ../lib/Analysis/LazyValueInfo.cpp:1993:13: warning: unused variable 'Impl' [-Wunused-variable]
  1993 |   if (auto *Impl = getImpl())
       |             ^~~~

Use the locals instead of calling getImpl() again.

Author: mikaelholmen

llvm/lib/Analysis/LazyValueInfo.cpp

@@ -1976,22 +1976,22 @@ void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
 
 void LazyValueInfo::forgetValue(Value *V) {
   if (auto *Impl = getImpl())
-    getImpl()->forgetValue(V);
+    Impl->forgetValue(V);
 }
 
 void LazyValueInfo::eraseBlock(BasicBlock *BB) {
   if (auto *Impl = getImpl())
-    getImpl()->eraseBlock(BB);
+    Impl->eraseBlock(BB);
 }
 
 void LazyValueInfo::clear() {
   if (auto *Impl = getImpl())
-    getImpl()->clear();
+    Impl->clear();
 }
 
 void LazyValueInfo::printLVI(Function &F, DominatorTree &DTree, raw_ostream &OS) {
   if (auto *Impl = getImpl())
-    getImpl()->printLVI(F, DTree, OS);
+    Impl->printLVI(F, DTree, OS);
 }
 
 // Print the LVI for the function arguments at the start of each basic block.