perf strlist: Allow substitutions from file contents in a given directory

So, if we have an strlist equal to:

   "file,close"

And we call it as:

   struct strlist_config *config = { .dirname = "~/strace/groups", };
   struct strlist *slist = strlist__new("file, close", &config);

And we have:
  $ cat ~/strace/groups/file
  access
  open
  openat
  statfs

Then the resulting strlist will have these contents:

  [ "access", "open", "openat", "statfs", "close" ]

This will be used to implement strace syscall groups in 'perf trace',
but can be used in some other tool, thus being implemented in 'strlist'.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-wi6l6qtomqlywwr6005jvs05@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/strlist.h

@@ -18,6 +18,7 @@ struct strlist {
 
 struct strlist_config {
 	bool dont_dupstr;
+	const char *dirname;
 };
 
 struct strlist *strlist__new(const char *slist, const struct strlist_config *config);
@@ -79,5 +80,5 @@ static inline struct str_node *strlist__next(struct str_node *sn)
 	for (pos = strlist__first(slist), n = strlist__next(pos); pos;\
 	     pos = n, n = strlist__next(n))
 
-int strlist__parse_list(struct strlist *slist, const char *s);
+int strlist__parse_list(struct strlist *slist, const char *s, const char *subst_dir);
 #endif /* __PERF_STRLIST_H */