selftests/bpf: Use portable POSIX basename()

Use the POSIX version of basename() to allow compilation against non-gnu
libc (e.g. musl). Include <libgen.h> ahead of <string.h> to enable using
functions from the latter while preferring POSIX over GNU basename().

In veristat.c, rely on strdupa() to avoid basename() altering the passed
"const char" argument. This is not needed in xskxceiver.c since the arg
is mutable and the program exits immediately after usage.
Signed-off-by: Tony Ambardar <tony.ambardar@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/0fd3c9f3c605e6cba33504213c9df287817ade04.1722244708.git.tony.ambardar@gmail.com

tools/testing/selftests/bpf/veristat.c

@@ -2,6 +2,7 @@
 /* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
 #define _GNU_SOURCE
 #include <argp.h>
+#include <libgen.h>
 #include <string.h>
 #include <stdlib.h>
 #include <sched.h>
@@ -988,8 +989,8 @@ static void fixup_obj(struct bpf_object *obj, struct bpf_program *prog, const ch
 
 static int process_prog(const char *filename, struct bpf_object *obj, struct bpf_program *prog)
 {
+	const char *base_filename = basename(strdupa(filename));
 	const char *prog_name = bpf_program__name(prog);
-	const char *base_filename = basename(filename);
 	char *buf;
 	int buf_sz, log_level;
 	struct verif_stats *stats;
@@ -1056,13 +1057,14 @@ static int process_prog(const char *filename, struct bpf_object *obj, struct bpf
 
 static int process_obj(const char *filename)
 {
+	const char *base_filename = basename(strdupa(filename));
 	struct bpf_object *obj = NULL, *tobj;
 	struct bpf_program *prog, *tprog, *lprog;
 	libbpf_print_fn_t old_libbpf_print_fn;
 	LIBBPF_OPTS(bpf_object_open_opts, opts);
 	int err = 0, prog_cnt = 0;
 
-	if (!should_process_file_prog(basename(filename), NULL)) {
+	if (!should_process_file_prog(base_filename, NULL)) {
 		if (env.verbose)
 			printf("Skipping '%s' due to filters...\n", filename);
 		env.files_skipped++;
@@ -1076,7 +1078,7 @@ static int process_obj(const char *filename)
 	}
 
 	if (!env.quiet && env.out_fmt == RESFMT_TABLE)
-		printf("Processing '%s'...\n", basename(filename));
+		printf("Processing '%s'...\n", base_filename);
 
 	old_libbpf_print_fn = libbpf_set_print(libbpf_print_fn);
 	obj = bpf_object__open_file(filename, &opts);

tools/testing/selftests/bpf/xskxceiver.c

@@ -90,6 +90,7 @@
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <libgen.h>
 #include <string.h>
 #include <stddef.h>
 #include <sys/mman.h>