Disable threadprivate data cleanup if runtime is terminating

The problem is due to the runtime's threadprivate cleanup code which tries to
access data that was already destroyed by one of the root threads.
__kmp_init_gtid is used as a checker here since it is set to false before actual
resource cleanup is done in __kmp_cleanup().

Patch by Hansang Bae

llvm-svn: 316452