Feat: ARMv7 support

[timfish]

• Allows libffi-rs to build for Raspberry Pi and other ARMv7 targets that don't have longdouble
• Fixes a failing test on Windows

[tov]

Thanks for the PR! This seems like a good thing to fix, but I wonder if there’s a simple way we could make it detect which types are available rather than having to specify the ABIs explicitly in the source…

[timfish]

I wonder if there’s a simple way we could make it detect which types are available

I'm open to suggestions but this is the only way I can think of!

[timfish]

It would be great to find a way to get something like this merged. I would like to publish a crate which depends on libffi but it won't build on Raspberry Pi and that's a platform we want to target.

I think it's safe to reduce the conditional compilation down to:

 #[cfg(not(target_arch = "arm"))]

The only other way I can think to do this is to parse the code generation output of libffi-sys and set a feature flag. It seems like this could be a lot more fragile that simply disabling longdouble support for arm. What other platforms don't support longdouble? Do we even have access to any of those platforms to test?

[yorickpeterse]

@timfish Now that 1.0.0 is released, could you rebase this MR and adjust if needed? I'd love to have these changes merged in 😄

[yorickpeterse]

@timfish Thanks!