Make struct dtors work in -betterC via hack on Linux

[adamdruppe]

They currently fail because they output a reference to druntime personality function. This hacks it out. Follow-up to my other PR: #6922

These together with Walter's at #6918 achieve the goal I set out in October to make -betterC actually usable.

Still a filthy hack, especially this one, but a usable filthy hack. We can go back and add stuff back in like EH later.

Note: I have not tested betterC on Windows yet. I think the struct dtor already works there though.

[adamdruppe]

It might make sense to suppress the generation of the call to _Unwind_Resume for now too... then you can make code that works with the libc as well. But we don't want to break it too much and code can always stub that out now.

[WalterBright]

I have not tested betterC on Windows yet. I think the struct dtor already works there though.

Sounds like a test case should be added to this PR!

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Bugzilla references

Fix	Bugzilla	Description
✓	17603	"undefined reference to `__dmd_personality_v0'" with -betterC and struct destructors

[CyberShadow]

@WalterBright Done

[adamdruppe]

And the tests are all passing. It doesn't quite work on Windows. I figure we can change it to use C++ library EH there, but the betterC flag wasn't available in nteh.c and #including it led to other errors! So I labeled this as being just Linux as a small step forward, better than nothing.

BTW on using C/C++ eh libs, I'm for that in general, though part of betterC's appeal to me is being able to pull out the C library too, so I say we want to keep that doable. not necessarily easy, but not harder than it needs to be either. Of course, that's a separate issue to this PR as it sits now which just hacks out the ref so we can use it today and worry about this later when we have a bit more real world experience.

[WalterBright]

Sorry, I haven't had a chance to look at this yet.

[MartinNowak]

In general we shouldn't merge behavior that only works on some platforms.

[adamdruppe]

betterC is itself a hack that only works on some platforms.

[WalterBright]

Superceded by #7305 and #7304