tsan: relaxed check in CheckShadowMapping

Some platforms use strange addresses in shadow mapping.
E.g. aarch64/42vma:
  static const uptr kHiAppMemEnd   = 0x3ffffffffffull;
instead of 0x40000000000ull (the range is half-open).
This caused bot failures after r282405:
http://lab.llvm.org:8011/builders/clang-cmake-aarch64-42vma/builds/12242/steps/ninja%20check%201/logs/FAIL%3A%20SanitizerCommon-tsan-aarch64-Linux%3A%3Aclock_gettime.c
Relaxed the new check in CheckShadowMapping to not expect round addresses.

llvm-svn: 282407