The error message held in {CompilationResult} was not null-terminated,
leading to ASan complaints. Just store it in a {std::string} and use
{c_str()} to get a properly null-terminated C-string.

Drive-by: Enable execution of the fuzzer tests.

R=ahaas@chromium.org

Bug: chromium:1334548, v8:12922
Change-Id: Iafcfd5ce77e49e2aa1ff0910d8718bcd51f83662
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3695356
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81020}