perf tools: Replace basename() calls with perf_basename()

perf tools: Replace basename() calls with perf_basename()

As noticed in a sashiko review for a patch adding a missing libgen.h
in a file using basename():

  https://sashiko.dev/#/patchset/20260402001740.2220481-1-acme%40kernel.org

So avoid these subtleties and instead reuse the gnu_basename() function
we had in srcline.c, renaming it to perf_basename() and replace
basename() calls with it, simplifying several cases by removing now
needless strdups.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>