[HIP] unbundle bundled preprocessor output

[HIP] unbundle bundled preprocessor output

There is a use case that users want to emit preprocessor
output as file and compile the preprocessor output later
with -x hip-cpp-output.

Clang emits bundled preprocessor output when users
compile with -E for combined host/device compilations.
Clang should be able to compile the bundled preprocessor
output with -x hip-cpp-output. Basically clang should
unbundle the bundled preprocessor output and launch
device and host compilation actions.

Currently there is a bug in clang driver causing bundled
preprocessor output not unbundled.

This patch fixes that.

Differential Revision: https://reviews.llvm.org/D92720