FROMLIST: selftests/timers: Guard LONG_MAX / LONG_MIN defines

Add ifndef guards around LONG_MAX / LONG_MIN defines. When building with
Android bionic, these macros are redefined because bionic's time.h will
include linux/time.h, which includes limit.h.

INFO: From Compiling common/tools/testing/selftests/timers/valid-adjtimex.c:
common/tools/testing/selftests/timers/valid-adjtimex.c:107:9: warning: 'LONG_MAX' macro redefined [-Wmacro-redefined]
  107 | #define LONG_MAX (~0UL>>1)
      |         ^
prebuilts/clang/host/linux-x86/clang-r522817/lib/clang/18/include/limits.h:47:9: note: previous definition is here
   47 | #define LONG_MAX  __LONG_MAX__
      |         ^
common/tools/testing/selftests/timers/valid-adjtimex.c:108:9: warning: 'LONG_MIN' macro redefined [-Wmacro-redefined]
  108 | #define LONG_MIN (-LONG_MAX - 1)
      |         ^
prebuilts/clang/host/linux-x86/clang-r522817/lib/clang/18/include/limits.h:52:9: note: previous definition is here
   52 | #define LONG_MIN  (-__LONG_MAX__ -1L)
      |         ^

Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Edward Liaw <edliaw@google.com>

Bug: 339526723
Link: https://lore.kernel.org/linux-kselftest/20240604231219.444603-1-edliaw@google.com/


Signed-off-by: Edward Liaw <edliaw@google.com>
(cherry picked from https://android-review.googlesource.com/q/commit:08172af5a61080c0b5fc2fea13611dd04697ef93)
Merged-In: Ia2e96dfbc6ae508330569359a7bbeb53e0131116
Change-Id: Ia2e96dfbc6ae508330569359a7bbeb53e0131116