SupportTests ProgramEnvTest.CreateProcessLongPath test is flaky on Windows

[rnk]

This test flaked for me in this build:
https://lab.llvm.org/buildbot/#/builders/146/builds/2701 (red)

It also flaked on this build:
https://lab.llvm.org/buildbot/#/builders/146/builds/2695 (red)

And passed on these two:
https://lab.llvm.org/buildbot/#/builders/146/builds/2702
https://lab.llvm.org/buildbot/#/builders/146/builds/2696

Logs will be gone soon, so here's what failure looks like:

******************** TEST 'LLVM-Unit :: Support/./SupportTests.exe/82/95' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:C:\a\lld-x86_64-win\build\unittests\Support\.\SupportTests.exe-LLVM-Unit-12424-82-95.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=95 GTEST_SHARD_INDEX=82 C:\a\lld-x86_64-win\build\unittests\Support\.\SupportTests.exe
--
Script:
--
C:\a\lld-x86_64-win\build\unittests\Support\.\SupportTests.exe --gtest_filter=ProgramEnvTest.CreateProcessLongPath
--
C:\a\lld-x86_64-win\llvm-project\llvm\unittests\Support\ProgramTest.cpp(160): error: Expected equality of these values:
  0
  RC
    Which is: -2
C:\a\lld-x86_64-win\llvm-project\llvm\unittests\Support\ProgramTest.cpp(163): error: fs::remove(Twine(LongPath)): did not return errc::success.
error number: 13
error message: permission denied
C:\a\lld-x86_64-win\llvm-project\llvm\unittests\Support\ProgramTest.cpp:160
Expected equality of these values:
  0
  RC
    Which is: -2
C:\a\lld-x86_64-win\llvm-project\llvm\unittests\Support\ProgramTest.cpp:163
fs::remove(Twine(LongPath)): did not return errc::success.
error number: 13
error message: permission denied
********************

I'm not sure what an exit code of -2 means.