This fixes a few leftovers where we use WASM_EXEC_TEST, but then
unconditionally execute the compiled code, and also changes more tests
to use WASM_EXEC_TEST, hence run in both the interpreter and compiled
code.
Once we have land the baseline compiler, those tests will also execute
in baseline compilation mode.

R=ahaas@chromium.org

Bug: v8:6600
Change-Id: I79598df21a7538934306e01ca6593f05afe19ed3
Reviewed-on: https://chromium-review.googlesource.com/672528
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48091}