This further reduces the amount of test-specific code. It will also
help testing the wasm baseline compiler, since it is also being called
from the {WasmCompilationUnit}.

Also, move the {RuntimeExceptionSupport} flag from the
{WasmFunctionCompiler} to the {TestingModuleBuilder}. There is no need
to store this per function builder. The {TestingModuleBuilder} then
passes it on to the {WasmCompilationUnit}, which finally sets it on the
{WasmGraphBuilder}.

R=mtrofin@chromium.org

Bug: v8:6600
Change-Id: I783dc296297a5ca37a2dd0d2035d782ca19a0fee
Reviewed-on: https://chromium-review.googlesource.com/660239
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Mircea Trofin <mtrofin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47970}