perf trace: Fix non-listed archs in the syscalltbl routines

This fixes a build breakage on 32-bit arm, where the
syscalltbl__id_at_idx() function was missing.

Committer notes:

Generating a proper syscall table from a copy of
arch/arm/tools/syscall.tbl ends up being too big a patch for this rc
stage, I started doing it but while testing noticed some other problems
with using BPF to collect pointer args on arm7 (32-bit) will maybe
continue trying to make it work on the next cycle...

Fixes: 7a2fb56 ("perf trace: Fix iteration of syscall ids in syscalltbl->entries")
Suggested-by: Howard Chu <howardchu95@gmail.com>
Signed-off-by: <jslaby@suse.cz>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Howard Chu <howardchu95@gmail.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/lkml/3a592835-a14f-40be-8961-c0cee7720a94@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: Jiri Slaby

tools/perf/util/syscalltbl.c

@@ -46,6 +46,11 @@ static const char *const *syscalltbl_native = syscalltbl_mips_n64;
 #include <asm/syscalls.c>
 const int syscalltbl_native_max_id = SYSCALLTBL_LOONGARCH_MAX_ID;
 static const char *const *syscalltbl_native = syscalltbl_loongarch;
+#else
+const int syscalltbl_native_max_id = 0;
+static const char *const syscalltbl_native[] = {
+	[0] = "unknown",
+};
 #endif
 
 struct syscall {
@@ -182,6 +187,11 @@ int syscalltbl__id(struct syscalltbl *tbl, const char *name)
 	return audit_name_to_syscall(name, tbl->audit_machine);
 }
 
+int syscalltbl__id_at_idx(struct syscalltbl *tbl __maybe_unused, int idx)
+{
+	return idx;
+}
+
 int syscalltbl__strglobmatch_next(struct syscalltbl *tbl __maybe_unused,
 				  const char *syscall_glob __maybe_unused, int *idx __maybe_unused)
 {