ci: skip -ldl on MinGW links; widen the gdb backtrace to the plugin test binaries

- oakffmpeg-link forwards pkg-config --static --libs verbatim; FFmpeg's
  .pc files can list -ldl via external deps, and MinGW has no libdl
- suites_test segfaults on the Linux runner too; run both plugin test
  binaries under gdb on test failure

.github/workflows/ci.yml

@@ -207,14 +207,16 @@ jobs:
         run: xvfb-run -a -s "-screen 0 1920x1080x24" cargo test --workspace --locked
 
       # A crashing (SIGSEGV) test gives no Rust backtrace; rerun the
-      # crashing binary under gdb to capture the native stack.
+      # plugin test binaries under gdb to capture the native stack.
       - name: Backtrace on test failure (Linux)
         if: failure()
         run: |
           sudo apt-get install -y gdb
-          BIN=$(ls -t target/debug/deps/node_e2e_test-* | grep -v '\.d$' | head -1)
-          xvfb-run -a gdb -batch -ex run -ex bt -- "$BIN" \
-            plugin_renders_constant_frame_end_to_end --exact --nocapture
+          for name in node_e2e_test suites_test; do
+            BIN=$(ls -t target/debug/deps/$name-* | grep -v '\.d$' | head -1)
+            [ -n "$BIN" ] || continue
+            xvfb-run -a gdb -batch -ex run -ex bt -- "$BIN" --nocapture || true
+          done
 
       - name: Test (macOS)
         if: runner.os == 'macOS'

crates/oakffmpeg-link/build.rs

@@ -102,6 +102,13 @@ fn main() {
 		if let Some(path) = token.strip_prefix("-L") {
 			println!("cargo:rustc-link-search=native={path}");
 		} else if let Some(lib) = token.strip_prefix("-l") {
+			// MinGW has no libdl: FFmpeg's .pc files can still list it via
+			// an external dep's Requires.private; the Unix dlopen surface
+			// the FFmpeg build uses has no Windows references to satisfy.
+			#[cfg(target_os = "windows")]
+			if lib == "dl" {
+				continue;
+			}
 			// System libs (m, z, bz2, iconv, ...) and externals alike; the
 			// linker picks .a or .dylib per -L search order.
 			println!("cargo:rustc-link-lib={lib}");