build: fix mksnapshot crash on sunos

Unconditionally compile V8 with -fno-strict-aliasing on all platforms.

gcc 4.5.2 on sunos generates bad code when -fstrict-aliasing is enabled, which
undoubtedly means that there are more buggy versions of gcc out there.

-fstrict-aliasing does not give a significant performance boost so let's just
disable it.

Fixes #3736.