We were previously reading a language mode from all comparison nodes
in JSGenericLowering::ReplaceWithCompareIC. This read was invalid for
{,Strict}{,Not}Equal nodes, as these nodes do not have a language mode, as they
derive from Operator rather than from Operator1<LanguageMode>. Because these
nodes are not language mode dependent, we arbitrarily pass Strength::WEAK
to CodeFactory::CompareIC.

Cleanup for cfi_vptr=1; see https://www.chromium.org/developers/testing/control-flow-integrity

BUG=chromium:457523
R=bmeurer@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/1319463003

Cr-Commit-Position: refs/heads/master@{#30491}