This patch introduces the AAP backend to LLVM.
AAP is a Harvard architecture, with features representative of a large range of deeply embedded microprocessors. It aims to aid the development and maintenance of other out-of-tree deeply embedded systems.
New backends should't be added to the default backend list. They should be added as experimental only.
Experimental backends are not specified in the CMake explicitly, you enable them by specifying them on the CMake command line with the variable LLVM_EXPERIMENTAL_TARGETS_TO_BUILD.