Found issue with BuildChangeEndianness. There is difference between load and store case.

Load depends primarily on MachineRepresentation, while store depends on ValueType.

TEST=wasm-spec-tests/tests/endianness
TEST=wasm-spec-tests/tests/memory
TEST=wasm-spec-tests/tests/memory_trap

Bug: 
Change-Id: I437f611107daad2f425a67fcc068e874822e0f58
Reviewed-on: https://chromium-review.googlesource.com/558882Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@imgtec.com>
Cr-Commit-Position: refs/heads/master@{#46645}