tools build: Build fixdep helper from perf and basic libs

Adding the fixdep target into the Makefile.include to ease up building of
fixdep helper, that needs to be built before we dive in to the build itself.
The user can invoke the fixdep target to build the helper.

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/1443004442-32660-8-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/build/Documentation/Build.txt

@@ -113,6 +113,13 @@ It defines following interface:
       make $(build)=ex
 
 
+Fixdep
+------
+It is necessary to build the fixdep helper before invoking the build.
+The Makefile.include file adds the fixdep target, that could be
+invoked by the user.
+
+
 Rules
 -----