[llvm] [ORC] Add AutoImportGenerator for COFF dllimport auto-import (PR #203914)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-darwin` running on `doug-worker-3` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/23/builds/21523

<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 :: ExecutionEngine/Orc/./OrcJITTests/1/10' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/unittests/ExecutionEngine/Orc/./OrcJITTests-LLVM-Unit-16178-1-10.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=10 GTEST_SHARD_INDEX=1 /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/unittests/ExecutionEngine/Orc/./OrcJITTests
--

Script:
--
/Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/unittests/ExecutionEngine/Orc/./OrcJITTests --gtest_filter=COFFAutoImportGeneratorTest.SynthesizesImpSlotAndThunk
--
/Users/buildbot/buildbot-root/x86_64-darwin/llvm-project/llvm/unittests/ExecutionEngine/Orc/COFFAutoImportGeneratorTest.cpp:112: Failure
Value of: llvm::detail::TakeExpected(ImpSym)
Expected: succeeded
  Actual: failed  (Symbols not found: [ __imp_getpid ])


/Users/buildbot/buildbot-root/x86_64-darwin/llvm-project/llvm/unittests/ExecutionEngine/Orc/COFFAutoImportGeneratorTest.cpp:112
Value of: llvm::detail::TakeExpected(ImpSym)
Expected: succeeded
  Actual: failed  (Symbols not found: [ __imp_getpid ])



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


```

</details>

https://github.com/llvm/llvm-project/pull/203914