Backend: Refine new instruction with IRBuilder create
Backend: Refine new instruction with IRBuilder create

New instruction changes with the llvm version but the IRbuilder
is more stables. So use IRBuilder create to make it can be built
with more llvm version.

V2: Change all alloca inst to the entry of the function.
Signed-off-by: Pan Xiuli <e5a665b1e626c5dc0826076a8b5a209eb48bf6ee@intel.com>
Reviewed-by: Ruiling Song <286a174c1339c6eff91abc41c3a1012c95030c95@intel.com>

wdv4758h/beignet,wdv4758h/beignet,wdv4758h/beignet,wdv4758h/beignet,wdv4758h/beignet