perf llvm: Use realpath to canonicalize paths

To kill the last user of make_nonrelative_path(), that gets ditched,
one more panicking function killed.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-3hu56rvyh4q5gxogovb6ko8a@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/Build

@@ -1,4 +1,3 @@
-libperf-y += abspath.o
 libperf-y += alias.o
 libperf-y += annotate.o
 libperf-y += build-id.o