tools include: Adopt strstarts() from the kernel

Replacing prefixcmp(), same purpose, inverted result, so standardize on
the kernel variant, to reduce silly differences among tools/ and the
kernel sources, making it easier for people to work in both codebases.

And then doing:

	if (strstarts(option, "no-"))

Looks clearer than doing:

	if (!prefixcmp(option, "no-"))

To figure out if option starts witn "no-".

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-kaei42gi7lpa8subwtv7eug8@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/lib/subcmd/help.c b/tools/lib/subcmd/help.c
index ba970a7..0310520 100644
--- a/tools/lib/subcmd/help.c
+++ b/tools/lib/subcmd/help.c
@@ -171,7 +171,7 @@ static void list_commands_in_dir(struct cmdnames *cmds,
 	while ((de = readdir(dir)) != NULL) {
 		int entlen;
 
-		if (prefixcmp(de->d_name, prefix))
+		if (!strstarts(de->d_name, prefix))
 			continue;
 
 		astrcat(&buf, de->d_name);