Combine main.cpp/main_cpp.cpp.

The only difference between aidl-cpp/aidl is the default language
specified in options (options adds more difference here). So that it's
easier to add code which always runs for any AIDL invocation, I've
removed main_cpp.cpp and used a define to distinguish the two builds.

Test: build
Change-Id: Ibc4a35d964180167c3d0c3c6f4a9c3cae9a14cd1
3 files changed