tools build: Fix objtool build with clang

tools build: Fix objtool build with clang

Clang doesn't support multiple arguments being passed to -Wp, so split
them.

  Fixes this error:
  HOSTCC   tools/objtool/fixdep.o
  cat: tools/objtool/.fixdep.o.d: No such file or directory

Signed-off-by: Peter Foley <pefoley2@pefoley.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20161128024346.17371-1-pefoley2@pefoley.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>