Fix tbb-compat linking after rename

[andrjohns]

Unsure if it's because of clang or windows arm64, but rstan models compiled against the current github RcppParallel fail at runtime with an error that tbb-compat.dll is not found - even though the DLL has been renamed to tbb.dll before being linked.

I believe this is because R CMD SHLIB generates a .def file when linking with the name of the DLL. Explicitly setting the output name to tbb.dll when calling R CMD SHLIB resolves the later runtime errors for me

[andrjohns]

It doesn't happen with the GCC-based x86_64 toolchain, but it does with the LLVM-based aarch64 toolchain - odd!

[kevinushey]

Thanks!