perf tools: Fix test build error when bindir contains double slash

When building with a prefix ending with a slash, for example:

	$ make prefix=/usr/local/

one of the perf tests fail to compile due to BUILD_STR macro mishandling
bindir_SQ string containing with two slashes:

	-DBINDIR="BUILD_STR(/usr/local//bin)"

with the following error:

	  CC       tests/attr.o
	tests/attr.c: In function ‘test__attr’:
	tests/attr.c:168:50: error: expected ‘)’ before ‘;’ token
	  snprintf(path_perf, PATH_MAX, "%s/perf", BINDIR);
                                                  ^
	tests/attr.c:176:1: error: expected ‘;’ before ‘}’ token
	 }
	 ^
	tests/attr.c:176:1: error: control reaches end of non-void function [-Werror=return-type]
	 }
	 ^
	cc1: all warnings being treated as errors

This patch works around the problem by "cleaning" the bindir string
using make's abspath function.

Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1438092613-21014-1-git-send-email-pawel.moll@arm.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>