GBE: Fix memdep-block-scan-limit caused bug on LLVM3.8
GBE: Fix memdep-block-scan-limit caused bug on LLVM3.8

Option memdep-block-scan-limit is added in LLVM3.8, and memdep block
limit is set on LLVM3.7. As we can not change the limit with LLVM3.7
there will still some bugs with LLVM3.7 if the limit was hint.

Signed-off-by: Pan Xiuli <e5a665b1e626c5dc0826076a8b5a209eb48bf6ee@intel.com>
Reviewed-by: Yang Rong <78759e37dc7114caed18f74e7515c5cb519dbf6d@intel.com>

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