tayga: fix compile on platforms with VFP

CFLAGS were set explicitly in configure.ac
and then got included in Makefile; remove them

fix compile error found on buildbot with arch sunxi

several compile errors on .o files:
 tayga uses VFP register arguments, nat64.o does not

Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>