Fix GNU import library for i386 architecture

[kleisauke]

For example, without this, attempting to use the generated import library results in the following errors:

/data/mxe/usr/bin/i686-w64-mingw32-ld: /data/mxe/usr/i686-w64-mingw32/lib/librav1e.dll.a(librav1e_dll_a_s00000.o):(.idata$7+0x0): undefined reference to `_head_librav1e_dll'
/data/mxe/usr/bin/i686-w64-mingw32-ld: /data/mxe/usr/i686-w64-mingw32/lib/librav1e.dll.a(librav1e_dll_a_s00001.o):(.idata$7+0x0): undefined reference to `_head_librav1e_dll'
/data/mxe/usr/bin/i686-w64-mingw32-ld: /data/mxe/usr/i686-w64-mingw32/lib/librav1e.dll.a(librav1e_dll_a_s00002.o):(.idata$7+0x0): undefined reference to `_head_librav1e_dll'
/data/mxe/usr/bin/i686-w64-mingw32-ld: /data/mxe/usr/i686-w64-mingw32/lib/librav1e.dll.a(librav1e_dll_a_s00003.o):(.idata$7+0x0): undefined reference to `_head_librav1e_dll'
/data/mxe/usr/bin/i686-w64-mingw32-ld: /data/mxe/usr/i686-w64-mingw32/lib/librav1e.dll.a(librav1e_dll_a_s00007.o):(.idata$7+0x0): undefined reference to `_head_librav1e_dll'
/data/mxe/usr/bin/i686-w64-mingw32-ld: /data/mxe/usr/i686-w64-mingw32/lib/librav1e.dll.a(librav1e_dll_a_s00011.o):(.idata$7+0x0): more undefined references to `_head_librav1e_dll' follow

and the same for *_iname symbol:

/data/mxe/usr/bin/i686-w64-mingw32-ld: /data/mxe/usr/i686-w64-mingw32/lib/librav1e.dll.a(librav1e_dll_a_h.o):fake:(.idata$2+0xc): undefined reference to `librav1e_dll_iname'

BTW, did you see https://github.com/rust-lang/ar_archive_writer? Rust uses it to generate MSVC/LLVM-style DLL import libraries for any raw-dylib functions.
https://github.com/rust-lang/rust/blob/1.84.0/compiler/rustc_codegen_ssa/src/back/archive.rs#L61-L132

Though, it will still fallback to dlltool from GNU Binutils for the *-windows-gnu targets.

[messense]

Not sure why but CI is failing on macOS.

[kleisauke]

I've updated the PR to address another minor compat issue when linking against the generated import library with LLVM.

Not sure why but CI is failing on macOS.

It looks like the CI only test the MSVC-style (aka. "short") import library, so the test failures are unrelated.