[OpenMP] Add thread ID function into new RTL

[jhuber6]

Summary

The new device runtime library currently lacks the
kmpc_get_hardware_thread_id_in_block function which is currently used
when doing the SPMDzation optimization. This call would be introduced
through the optimization and then cause a linking error because it was
not present. This patch adds support for this runtime call.

[tianshilei1992]

LG

openmp/libomptarget/DeviceRTL/include/Interface.h

 void __kmpc_end_sharing_variables();
 
 /// Store the allocation address obtained via __kmpc_begin_sharing_variables in
 /// \p GlobalArgs.
 ///
 /// Called by the worker threads in the parallel region (function).
 void __kmpc_get_shared_variables(void ***GlobalArgs);
 
+/// External interface to get the thread ID.
+uint32_t __kmpc_get_hardware_thread_id_in_block();
+
 /// Kernel
 ///
 ///{
 int8_t __kmpc_is_spmd_exec_mode();
 
 int32_t __kmpc_target_init(IdentTy *Ident, bool IsSPMD,
                            bool UseGenericStateMachine, bool);
 

openmp/libomptarget/DeviceRTL/src/Mapping.cpp

if (!mapping::getThreadIdInBlock())
     IsSPMDMode = IsSPMD;
 }
 
 bool mapping::isSPMDMode() { return IsSPMDMode; }
 
 bool mapping::isGenericMode() { return !isSPMDMode(); }
 ///}
 
+extern "C" {
+uint32_t __kmpc_get_hardware_thread_id_in_block() {
+  return mapping::getThreadIdInBlock();
+}
+}
 #pragma omp end declare target