Add debuginfo flags for msvc assemblers

[nagisa]

When code is being built with debuginfo, we need to instruct the assemblers accordingly.

[thomcc]

This matches the documentation on the arm assemblers https://learn.microsoft.com/en-us/cpp/assembler/arm/arm-assembler-command-line-reference?view=msvc-170

The x86 arg seems a bit odd tho https://learn.microsoft.com/en-us/cpp/assembler/masm/ml-and-ml64-command-line-reference?view=msvc-170, but maybe it's just a lack of familiarity with the term "CodeView" for a debuginfo format.

I don't have a good way to test this at the moment, so I might punt to @ChrisDenton in case he's slightly more familiar than I.

[nagisa]

FWIW my approach to testing this was basically just slapping a cmd.arg("-Zi") in my build.rs and running my stuffs in a debugger.

Two things to keep in mind when interpreting this change for x86: this flag is somewhat shared between the ml assembler and the c/c++ compiler (cl), though it seems to be closer to /Z7: https://learn.microsoft.com/en-us/cpp/build/reference/z7-zi-zi-debug-information-format?view=msvc-170

And / is interchangeable with -. Since cc-rs appears to be using -, I stuck to that convention as well.

[ChrisDenton]

This does look correct to me but I'll test when I have a moment.

[ChrisDenton]

Ok, I tested in WinDbg. With this patch I get an interactive code view when debugging, which is a very nice enhancement!

Btw, it'd be good if CI were able to test debugging info in a similar way to the main rust repo. But setting that up is way beyond the scope of this PR.