tools build: Make the .cmd file more readable

Putting extra line between dependencies and cmd_* definition
to make it more readable.

Before:

  $ cat .builtin-top.o.cmd
  ...
  /home/jolsa/kernel/linux-perf/tools/include/linux/stringify.h \
  /home/jolsa/kernel/linux-perf/tools/include/linux/time64.h
  cmd_builtin-top.o := gcc -Wp,-MD,./.builtin-top.o.d -Wp,-MT,builtin-...
  ...

After:

  $ cat .builtin-top.o.cmd
  ...
  /home/jolsa/kernel/linux-perf/tools/include/linux/stringify.h \
  /home/jolsa/kernel/linux-perf/tools/include/linux/time64.h

  cmd_builtin-top.o := gcc -Wp,-MD,./.builtin-top.o.d -Wp,-MT,builtin-...
  ...
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1480884178-8072-2-git-send-email-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/build/Build.include

@@ -65,7 +65,7 @@ dep-cmd = $(if $(wildcard $(fixdep)),
            printf '\# cannot find fixdep (%s)\n' $(fixdep) > $(dot-target).cmd; \
            printf '\# using basic dep data\n\n' >> $(dot-target).cmd;           \
            cat $(depfile) >> $(dot-target).cmd;                                 \
-           printf '%s\n' 'cmd_$@ := $(make-cmd)' >> $(dot-target).cmd)
+           printf '\n%s\n' 'cmd_$@ := $(make-cmd)' >> $(dot-target).cmd)
 
 ###
 # if_changed_dep  - execute command if any prerequisite is newer than