tsan: use MADV_NOHUGEPAGE only if it is supported by platform
Fixes build failure on an old system:
http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-centos-6.5/builds/7555/steps/build/logs/stdio



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@214394 91177308-0d34-0410-b5e6-96231b3b80d8