This uses an optimized single-byte encoding for WASM_STUB_CALL reloc
entries when possible, by sacrificing size from DEOPT_REASON. Note that
stub calls in WebAssembly are used for trap handlers, which are fairly
common on regular WasmCode.

R=clemensh@chromium.org
BUG=chromium:850111,chromium:850413

Change-Id: I153fdd775290dece2884d438d5defd441486b369
Reviewed-on: https://chromium-review.googlesource.com/1090831
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53587}