[x86/Linux] Revises exception handling macros for x86/Linux

[parjong]

This commit revises exception handling macros similarly as amd64/Linux.

[parjong]

\CC @seanshpark

[janvorli]

@parjong seeing the several recent changes in the exception handling related stuff, I am worried that after deciding to not to try to define the WIN64EXCEPTIONS, we are heading into the same mess we were trying to avoid, this time with trying to ifdef out chunks of x86 style exception handling code.
My worry is that some functions that we ifdef out are needed by some other code and we either didn't get to the point when a caller gets compiled or that there are prototypes of the excluded functions that keep the compiler happy, but we will hit the problem later when we'll be trying to make everything link together without missing symbols.
We are also polluting the code base with a lot of ifdefs that we will want to remove after we switch to WIN64EXCEPTIONS later. And it would be a pain to keep track of where have we put them.
So I would like us to pause and see if we can rather make most of the x86 exception handling code build on Unix and add dummy structs / stubbed out implementation of Windows APIs that the code uses(if any) to unixstubs.cpp so that we can remove them later easily.
@jkotas does it make sense to you too?

[jkotas]

if we can rather make most of the x86 exception handling code build on Unix and add dummy structs / stubbed out implementation of Windows APIs that the code uses(if any) to unixstubs.cpp so that we can remove them later easily.

I agree. It is hard to tell whether the changes like this one are going in the right direction without seeing the more complete picture.

[parjong]

@janvorli @jkotas While working on x86/Linux port, I also feel that there is some unclear ifdef. IMHO, #8372 may be such an example.

I currently try both approaches (with/without WIN64EXCEPTIONS), and feel that both directions require some code cleanup.

[jkotas]

I would recommend to focus on without WIN64EXCEPTIONS for the time being. It will get you to a working hello world much faster.

Note that we had a working MacOS x86 port before for Silverlight browser plugin. It was on without WIN64EXCEPTIONS plan. If you stay on the without WIN64EXCEPTIONS you are basically just fixing bit rot and catching up with changes that happened since then. This territory was fully explored before.

The with WIN64EXCEPTIONS plan is unexplored territory for x86.

[parjong]

@jkotas I'll focus on that approach. Thank you.

[parjong]

The recent changes require the revision of this PR. I'll re-open this PR or submit a new PR when it is ready.