Work around rustc bug by ignoring debug = true in Cargo.toml on x86_64-pc-windows-msvc only

[briansmith]

The rustc bug is rust-lang/rust#29413.

My plan is to write a patch for Cargo that will skip passing the -g flag on x86_64-pc-windows-msvc release mode builds only, even when debug = true is specified, until the rustc bug is fixed. This will allow people to use debug = true in release builds in their Cargo.toml and get the expected results, except on this one platform. Right now, we just can't use debug = true in such configurations.

Does this seem reasonable, @alexcrichton? If so, I'll write the patch.

[alexcrichton]

It looks like disabling LTO also causes this to link correctly, so perhaps that could be the solution for now? LTO's already off by default thankfully at least!

[briansmith]

Right, that's why it probably hasn't been reported until now. But, my libraries use LTO and I don't want to turn it off LTO all platforms just to work around this bug on x86_64-pc-windows-msvc. I'd rather turn off debugging instead. But, a workaround targetted specifically to x86_64-pc-windows-msvc still seems best to me.

[alexcrichton]

Due to the fact that compiles "work by default" today I'm hesitant to bake this kind of logic into Cargo at least, it seems more appropriate in the compiler. I guess debuginfo could be disabled with LTO on 64-bit msvc, or stripped somehow?

[briansmith]

at least, it seems more appropriate in the compiler.

OK, that sounds reasonable to me.