Add createLocalVariableDefinitions

This function is used to create GPU local variables, i.e. for shared
memory array or private memory definitions.
 + Add static function getLLVMTypeByName - use this function to get
   the llvm::Type of a type string. (This is a ugly and temporary
   solution.)
Add createKernelCopy function

This function is use to create LLVM IR for copy statement in a kernel
when shared memory or private memory code generation is enabled.
Add eraseSharedMemoryBases

This function is used to erase all the allocated shared memory from the
host module after the complete of the GPGPU code generation.
[Fix] Fix extractArraysInfo in case array base not Global Variable
Update for llvm::DataLayoutPass changes.
Update for llvm api changes
[Fix] Get the address of the access expression
Add comments when initializing fields of ppcg_debug_options
Enable private memory code generation