gollvm: sync with trunk at a61fa1a4b9d

Update bridge to handle new restrictions on llvm::Constant::deleteValue().

Change-Id: Ifb9dedb951a1c40b165e85337283f52fe265ef2a
Reviewed-on: https://go-review.googlesource.com/c/gollvm/+/240684
Reviewed-by: Cherry Zhang <cherryyz@google.com>

bridge/go-llvm.cpp

diff --git a/bridge/go-llvm.cpp b/bridge/go-llvm.cpp
index 92c0f54..630a49a 100644
--- a/bridge/go-llvm.cpp
+++ b/bridge/go-llvm.cpp
@@ -2752,7 +2752,10 @@
       llvm::Constant *newDeclVal = llvm::cast<llvm::Constant>(
           module_->getOrInsertFunction(fn, declFnTyp).getCallee());
       declFnVal->replaceAllUsesWith(newDeclVal);
-      declFnVal->deleteValue();
+      // NB: previously we had a call to declFnVal->deleteValue() here, but this
+      // appears to no longer be supported, and declFnVal->destroyConstant()
+      // results in an assert. For now leave the old constant around, just
+      // remove references to it.
       for (auto it = fcnDeclMap_.begin(); it != fcnDeclMap_.end(); it++) {
         if (it->first.second.compare(fns) == 0) {
           Bfunction *found = it->second;