[llvm-dev] Ninja build (on Windows anyway) may be doing redundant work

[via llvm-dev]

This afternoon I did a clean build of llvm using ninja and MSVC 2015 on
Windows 10. I saw something curious and wondered if any of the ninja or
CMake experts out there can explain/fix it.

[2663/3121] Linking CXX shared library bin\LTO.dll
   Creating library lib\LTO.dll and object lib\LTO.exp
   Creating library lib\LTO.dll and object lib\LTO.exp
[3120/3121] Running the LLVM regression tests
[[[ etc ]]]

I'm curious about the "creating library" message popping out twice.
Sometimes ninja builds will die on me, complaining about a corrupted
object file, usually related to LTO. Rerunning ninja usually completes
successfully.  So I wonder if there's some mishap in the dependencies
somewhere that actually causes the build to try to link the DLL twice,
which of course might corrupt a file if the links are overlapping in
time.

Thought I'd throw this out there in case someone wants to take a look.
--paulr