libclc: Use temporary files rather than a pipe

This is required for using the Ninja backend on Windows, as it passes
commands directly to CreateProcess, and does not allow the shell to
interpret them: https://ninja-build.org/manual.html#ref_rule_command

Using the Visual Studio backend is not possible as attempting to create
a static library target comprised entirely of novel languages not known
to the Visual Studio backend built in to CMake's C++ source will
generate nothing at all.

reviewer: jvesely
Differential Revision: https://reviews.llvm.org/D77165