Hangs while building with Windows using SwiftPM

[cmcgee1024]

When building using SwiftPM and the swiftbuild build system there are frequent hangs.

From the swift-package manager repo, run this command on Windows x86_64:

swift run swift-build --build-system=swiftbuild Fixtures/ValidLayouts/SingleModule/ExecutableNew

See that attached text file with the sampled stack traces. Many of the interesting ones appear to be in swift-build spec registration (SpecRegistry.registerSpec) and file path handling. Note that these samples are taken across multiple invocations, since the target process is tending to crash frequently when stopped in lldb.

Process 23424 stopped.txt