[OpenMP][Tool] Runtime warning for missing TSan-option

TSan spuriously reports for any OpenMP application a race on the initialization
of a runtime internal mutex:

```
Atomic read of size 1 at 0x7b6800005940 by thread T4:
  #0 pthread_mutex_lock <null> (a.out+0x43f39e)
  #1 __kmp_resume_64 <null> (libomp.so.5+0x84db4)

Previous write of size 1 at 0x7b6800005940 by thread T7:
  #0 pthread_mutex_init <null> (a.out+0x424793)
  #1 __kmp_suspend_initialize_thread <null> (libomp.so.5+0x8422e)
```

According to @AndreyChurbanov this is a false positive report, as the control
flow of the runtime guarantees the ordering of the mutex initialization and
the lock:
https://software.intel.com/en-us/forums/intel-open-source-openmp-runtime-library/topic/530363

To suppress this report, I suggest the use of
TSAN_OPTIONS='ignore_uninstrumented_modules=1'.
With this patch, a runtime warning is provided in case an OpenMP application
is built with Tsan and executed without this Tsan-option.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D70412

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