trace: use standard POSIX header for basename()

trace: use standard POSIX header for basename()

The musl libc only implements POSIX basename() but provided a GNU header
kludge in <string.h>, which was removed in musl 1.2.5 [1]. Use the standard
<libgen.h> header to avoid compilation errors like:

trace/trace.c: In function 'main':
trace/trace.c:435:64: error: implicit declaration of function 'basename';
did you mean 'rename'? [-Werror=implicit-function-declaration]
  435 | if (asprintf(&json, "/tmp/%s.%u.json", basename(*argv), child) < 0)
      |                                        ^~~~~~~~
      |                                        rename
cc1: all warnings being treated as errors

Link 1: https://git.musl-libc.org/cgit/musl/log/?qt=grep&q=basename

Signed-off-by: Tony Ambardar <itugrok@yahoo.com>