[llvm] Reland "Add a pass to collect dropped var stats for MIR" (PR #117044)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-sie-ubuntu-fast` running on `sie-linux-worker` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/144/builds/13034

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

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM-Unit :: CodeGen/./CodeGenTests/19/39' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/unittests/CodeGen/./CodeGenTests-LLVM-Unit-1924373-19-39.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=39 GTEST_SHARD_INDEX=19 /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/unittests/CodeGen/./CodeGenTests
--

Note: This is test shard 20 of 39.
[==========] Running 8 tests from 8 test suites.
[----------] Global test environment set-up.
[----------] 1 test from AArch64SelectionDAGTest
[ RUN      ] AArch64SelectionDAGTest.getSplatSourceVector_Fixed_ADD_of_BUILD_VECTOR
/home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/llvm/unittests/CodeGen/AArch64SelectionDAGTest.cpp:44: Skipped


[  SKIPPED ] AArch64SelectionDAGTest.getSplatSourceVector_Fixed_ADD_of_BUILD_VECTOR (0 ms)
[----------] 1 test from AArch64SelectionDAGTest (0 ms total)

[----------] 1 test from AsmPrinterEmitDwarfLengthOrOffsetTest
[ RUN      ] AsmPrinterEmitDwarfLengthOrOffsetTest.DWARF64
[       OK ] AsmPrinterEmitDwarfLengthOrOffsetTest.DWARF64 (0 ms)
[----------] 1 test from AsmPrinterEmitDwarfLengthOrOffsetTest (0 ms total)

[----------] 1 test from DroppedVariableStatsMIR
[ RUN      ] DroppedVariableStatsMIR.ChildScopes

--
exit: -11
--
shard JSON output does not exist: /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/unittests/CodeGen/./CodeGenTests-LLVM-Unit-1924373-19-39.json
********************


```

</details>

https://github.com/llvm/llvm-project/pull/117044