Reloc info often means that the constant will be patched later, and for
this patching we have to make sure that there is enough space in the
code for the new value.

R=bmeurer@chromium.org, titzer@chromium.org, gdeepti@chromium.org
BUG=chromium:684407
TEST=cctest/test-assembler-x64/Regression684407

Review-Url: https://codereview.chromium.org/2655213003
Cr-Commit-Position: refs/heads/master@{#42719}