[llvm] IRLinker: avoid quadratic behavior (PR #157045)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `cross-project-tests-sie-ubuntu` running on `doug-worker-1a` while building `llvm` at step 6 "test-build-unified-tree-check-cross-project".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/181/builds/27321

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-cross-project) failure: test (failure)
******************** TEST 'cross-project-tests :: debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_after_ref.cpp' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
clang++ -O0 -glldb -std=gnu++11 /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/llvm-project/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_after_ref.cpp -o /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/build/projects/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/Output/address_after_ref.cpp.tmp # RUN: at line 5
+ clang++ -O0 -glldb -std=gnu++11 /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/llvm-project/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_after_ref.cpp -o /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/build/projects/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/Output/address_after_ref.cpp.tmp
"/usr/bin/python3.8" "/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/llvm-project/cross-project-tests/debuginfo-tests/dexter/dexter.py" test --fail-lt 1.0 -w --debugger lldb-dap --lldb-executable "/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/build/bin/lldb-dap" --binary /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/build/projects/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/Output/address_after_ref.cpp.tmp -- /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/llvm-project/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_after_ref.cpp | /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/build/bin/FileCheck /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/llvm-project/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_after_ref.cpp # RUN: at line 6
+ /usr/bin/python3.8 /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/llvm-project/cross-project-tests/debuginfo-tests/dexter/dexter.py test --fail-lt 1.0 -w --debugger lldb-dap --lldb-executable /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/build/bin/lldb-dap --binary /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/build/projects/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/Output/address_after_ref.cpp.tmp -- /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/llvm-project/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_after_ref.cpp
+ /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/build/bin/FileCheck /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/llvm-project/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_after_ref.cpp


****************************************


```

</details>

https://github.com/llvm/llvm-project/pull/157045