Convert libbcc to Android.bp

See build/soong/README.md for more information.

Includes one small code change to replace
FORCE_BUILD_LLVM_DISABLE_NDEBUG with _DEBUG, which is set already in
llvm-defaults in external/llvm/soong/llvm.go when the environment
variable is set.

libbcc-targets.mk remains, it is still used by frameworks/rs/cpu_ref.

Test: mma -j
Test: mma -j FORCE_BUILD_LLVM_COMPONENTS=true
Change-Id: Iec37d2c33020bb5702c27497ae343a8312601202