Remove -Wno-invalid-offsetof from compilation flags

[andreiltd]

As mentioned here: https://github.com/bytecodealliance/StarlingMonkey/pull/242#issuecomment-3201119743 we should re-enable this warning and use suppression maps from clang:

https://clang.llvm.org/docs/WarningSuppressionMappings.html

# .clang-suppression:
# Suppress -Winvalid-offsetof warnings in SpiderMonkey
[invalid-offsetof]
src:*/spidermonkey-debug/*
src:*/spidermonkey-release/*

This will be possible when we update to the version of wasi-sdk with clang version >=20