On 32-bit systems FXXXConvertI64 instructions are compiled to calls to
C functions. The TF node for the function call is already generated in
the wasm compiler, the lowering of the I64 parameter is done in the
Int64Lowering.

R=titzer@chromium.org, yangguo@chromium.org

Review URL: https://codereview.chromium.org/1738623003

Cr-Commit-Position: refs/heads/master@{#34487}