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 <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/build/Build.include

···
            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)
 
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 # if_changed_dep  - execute command if any prerequisite is newer than