[IR] Ignore the return value of std::remove_if (NFC)

/Users/jiefu/llvm-project/llvm/lib/IR/Instructions.cpp:166:3: error: ignoring return value of function declared with 'nodiscard' attribute [-Werror,-Wunused-result]
  std::remove_if(const_cast<block_iterator>(block_begin()),
  ^~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

Author: DamonFool

llvm/lib/IR/Instructions.cpp

@@ -163,7 +163,7 @@ void PHINode::removeIncomingValueIf(function_ref<bool(unsigned)> Predicate,
     U.set(nullptr);
 
   // Remove incoming blocks.
-  std::remove_if(const_cast<block_iterator>(block_begin()),
+  (void)std::remove_if(const_cast<block_iterator>(block_begin()),
                  const_cast<block_iterator>(block_end()), [&](BasicBlock *&BB) {
                    return RemoveIndices.contains(&BB - block_begin());
                  });