This makes sure that reloc entries with WASM_STUB_CALL mode can be
shared within the constant pool. Call sites to such stubs never need to
be patched individually and absolute addresses of such call targets can
be shared when they are put into constant pools.

This applies to ARM, ARM64 and PPC architectures only.

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

Change-Id: I657248f61f122f1a3d6d30ebd14326df45f67540
Reviewed-on: https://chromium-review.googlesource.com/1091055Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53603}