selftests/harness: remove use of LINE_MAX

Android was seeing a compliation error because its C library does not
define LINE_MAX.  This replaces the use of LINE_MAX / snprintf with
asprintf, which will change the behavior to not truncate the test name if
it is over 2048 chars long.

See also:
https://github.com/llvm/llvm-project/issues/88119

[akpm@linux-foundation.org: remove limits.h include, per Edward]
[akpm@linux-foundation.org: check asprintf() return]
[usama.anjum@collabora.com: fix undeclared function error]
  Link: https://lkml.kernel.org/r/20240417075530.3807625-1-usama.anjum@collabora.com
Link: https://lkml.kernel.org/r/20240411231954.62156-1-edliaw@google.com
Fixes: 38c957f0

 ("selftests: kselftest_harness: generate test name once")
Signed-off-by: Edward Liaw <edliaw@google.com>
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Bill Wendling <morbo@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Edward Liaw <edliaw@google.com>
Cc: Justin Stitt <justinstitt@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: "Mike Rapoport (IBM)" <rppt@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Will Drewry <wad@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>