[SYCL] Skip processKernel for declarations in LocalAccessorToSharedMemory

ed022d9 start to enable partitions in LTO.
So the input IR to LocalAccessorToSharedMemory might contains
delarations only, we should skip such functions.
Or else we will get into assertsions or segv when getting entryblock.

Author: jsji

llvm/lib/SYCLLowerIR/LocalAccessorToSharedMemory.cpp

@@ -86,6 +86,9 @@ LocalAccessorToSharedMemoryPass::run(Module &M, ModuleAnalysisManager &) {
 
 Function *LocalAccessorToSharedMemoryPass::processKernel(Module &M,
                                                          Function *F) {
+  if (F->isDeclaration())
+    return nullptr;
+
   // Check if this function is eligible by having an argument that uses shared
   // memory.
   const bool UsesLocalMemory =