Cannot link static libraries on Windows MinGW because the Libs.private flags are ignored

[amyspark]

Hi,

I'm testing GStreamer's gst-plugins-rs integration in Windows. I got a linker failure when linking against the GStreamer bindings, which does not seem to have an apparent cause (logs in the gist here, since the linker line is massive).

However, upon looking at the reference to CoTaskMemFree, I recalled I'd seen this failure before when testing nuwen.net's flavor of GCC. The probe code here:

pkg-config-rs/src/lib.rs

Lines 395 to 404 in 576f550

	let output = self
	.run(name, &["--libs", "--cflags"])
	.map_err(|e| match e {
	Error::Failure { command, output } => Error::ProbeFailure {
	name: name.to_owned(),
	command,
	output,
	},
	other => other,
	})?;

never checks if the library being linked is dynamic or static. If it's the latter, then the objects in Libs.private need to be taken into account, and the --static flag must be passed to pkg-config. Otherwise, those symbols are never resolved. I believe this was written implicitly assuming the ELF model of static libraries.

cc @nirbheek