[OpenMP] libomp: Fix build with LIBOMP_STATS=ON on x86

[t-msn]

Summary

It seems llvm build uses -Werror=date-time by defalt since
ead0b76382a5a, so remove DATE__/TIME__ macro to build
successfully when LIBOMP_STATS=ON on x86.

openmp/runtime/src/kmp_stats.cpp

if (__kmp_cpuinfo.frequency == 0)
     fprintf(statsOut, "# Nominal frequency: Unknown\n");
   else
     fprintf(statsOut, "# Nominal frequency: %sz\n",
             formatSI(double(__kmp_cpuinfo.frequency), 9, 'H').c_str());
   outputEnvVariable(statsOut, "KMP_HW_SUBSET");
   outputEnvVariable(statsOut, "KMP_AFFINITY");
   outputEnvVariable(statsOut, "KMP_BLOCKTIME");
   outputEnvVariable(statsOut, "KMP_LIBRARY");
-  fprintf(statsOut, "# Production runtime built " __DATE__ " " __TIME__ "\n");
 #endif
 }
 
 void kmp_stats_output_module::outputStats(const char *heading) {
   // Stop all the explicit timers in all threads
   // Do this before declaring the local statistics because thay have
   // constructors so will take time to create.
   windupExplicitTimers();