Spurious failure removing std.dll during tests on MSVC

[alexcrichton]

First witnessed at https://ci.appveyor.com/project/rust-lang/rust/build/1.0.2679/job/wan951duah2q7d3q

looks like:

[02:11:03] 	finished in 57.500
[02:11:03] Testing libstd stage2 (x86_64-pc-windows-msvc -> x86_64-pc-windows-msvc)
[02:11:05]    Compiling cmake v0.1.22
[02:11:05]    Compiling alloc v0.0.0 (file:///C:/projects/rust/src/liballoc)
[02:11:09]    Compiling rustc_lsan v0.0.0 (file:///C:/projects/rust/src/librustc_lsan)
[02:11:10]    Compiling rustc_asan v0.0.0 (file:///C:/projects/rust/src/librustc_asan)
[02:11:10]    Compiling rand v0.0.0 (file:///C:/projects/rust/src/librand)
[02:11:11]    Compiling rustc_msan v0.0.0 (file:///C:/projects/rust/src/librustc_msan)
[02:11:12]    Compiling rustc_tsan v0.0.0 (file:///C:/projects/rust/src/librustc_tsan)
[02:11:12]    Compiling core v0.0.0 (file:///C:/projects/rust/src/libcore)
[02:11:15]    Compiling collections v0.0.0 (file:///C:/projects/rust/src/libcollections)
[02:12:17]    Compiling std v0.0.0 (file:///C:/projects/rust/src/libstd)
[02:12:18] error: failed to remove: C:\projects\rust\build\x86_64-pc-windows-msvc\stage1-std\x86_64-pc-windows-msvc\release\std.dll
[02:12:18] Build failed, waiting for other jobs to finish...
[02:15:01] error: build failed

No idea what's going on :(

[nagisa]

As with all removal failures on windows, something had it open at the time of deletion.

[retep998]

We really need to add more retries internally to rustc and cargo. Stuff like this gets hit a lot by people building code on network drives, due to operations not actually being done by the time the function returns. Every time we create a file and then delete it or we delete a file and then create it or other such sequential operations, we should have a retry loop that tries a couple times with a short sleep after each attempt.

[kennytm]

This spurious failure affects x86_64-pc-windows-gnu as well, not just MSVC.