Lowering of Int64Load, Int64Store, BitcastInt64ToFloat64 and
BitcastFloat64ToInt64 was using LE word ordering in memory,
causing failures on some tests.

BUG=mjsunit/regress/regress-599719,mjsunit/regress/regress-599717

Review-Url: https://codereview.chromium.org/2080213004
Cr-Commit-Position: refs/heads/master@{#37213}