llvm: Consolidate .inc files

* unlike other recipes where we have a rule to keep only one
  version, llvm is different so we'll keep .inc files
* llvm.inc is shared by all, llvm[23].inc are separated because
  2.* is built with cmake and 3.* with automake
* fix staticdev packaging and move it to shared llvm.inc
  FILES_${PN}-static-dev = "${libdir}/${LLVM_DIR}/*.a"
  (it's staticdev not static-dev)

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>