Remove dependency on arm_neon.h

Remove the global clang dependency on arm_neon.h and the rules to
generate arm_neon.h, they are left over from when $(CLANG) might point
to a locally built copy of clang and are superseded by
clang-tblgen-rules.mk.  Fixes a circular dependency between clang,
clang-tblgen, and arm_neon.h.

Bug: 25874490
Change-Id: I0e6b5e04c4a72d2aaaf4ce63b62a09caf5a40fc9
2 files changed