bfin: handle BFIN_CPU_UNKNOWN in TARGET_CPU_CPP_BUILTINS

bfin: handle BFIN_CPU_UNKNOWN in TARGET_CPU_CPP_BUILTINS

gcc/c-family/c-cppbuiltin.c
In file included from ./tm.h:21:0,
                 from
../../../../../../home/me/src/gcc-5.0.mine/gcc/c-family/c-cppbuiltin.c:23:
../../../../../../home/me/src/gcc-5.0.mine/gcc/c-family/c-cppbuiltin.c:
In function ‘void c_cpp_builtins(cpp_reader*)’:
../../../../../../home/me/src/gcc-5.0.mine/gcc/config/bfin/bfin.h:43:14:
error: enumeration value ‘BFIN_CPU_UNKNOWN’ not handled in switch
[-Werror=switch]
       switch (bfin_cpu_type)   \
              ^
../../../../../../home/me/src/gcc-5.0.mine/gcc/c-family/c-cppbuiltin.c:1243:3:
note: in expansion of macro ‘TARGET_CPU_CPP_BUILTINS’
   TARGET_CPU_CPP_BUILTINS ();
   ^
cc1plus: all warnings being treated as errors
make[2]: *** [c-family/c-cppbuiltin.o] Error 1

Maybe seeing BFIN_CPU_UNKNOWN in the cpu switch statement should
__builtin_abort() but be conservative to just allow all-gcc of config-list.mk
to compile

From-SVN: r222307