[DebugInfo][RemoveDIs] Erase ranges of instructions individually (#81007)

The BasicBlock::erase method simply removes a range of instructions from
the instlist by unlinking them. However, now that we're attaching
debug-info directly to instructions, some cleanup is required, so use
eraseFromParent on each instruction instead.

This is less efficient, but rare, and seemingly only WASM EH Prepare
uses this method of BasicBlock. Detected via a memory leak check in
asan.

(asan is always the final boss for whatever I do).

Author: jmorse

llvm/lib/IR/BasicBlock.cpp

@@ -677,7 +677,9 @@ BasicBlock *BasicBlock::splitBasicBlockBefore(iterator I, const Twine &BBName) {
 
 BasicBlock::iterator BasicBlock::erase(BasicBlock::iterator FromIt,
                                        BasicBlock::iterator ToIt) {
-  return InstList.erase(FromIt, ToIt);
+  for (Instruction &I : make_early_inc_range(make_range(FromIt, ToIt)))
+    I.eraseFromParent();
+  return ToIt;
 }
 
 void BasicBlock::replacePhiUsesWith(BasicBlock *Old, BasicBlock *New) {