ci(session-e2e): wrap zig in single-binary cgo launchers for Windows

The Windows link failed with 'fork/exec zig.exe: The filename or
extension is too long' (Win error 206). The cgo build links ~560 object
files whose paths overflow Windows' command-line limit. Go writes link
args to a @response file when they're too long, but only after probing
that the linker accepts @file -- and that probe runs only argv[0] of
$CC. With CC="zig cc -target ...", argv[0] is bare 'zig' (no 'cc'
subcommand), so the probe fails, Go skips the response file, and the
argv overflows.

Build zcc.exe/zxx.exe launchers that forward to 'zig cc'/'zig c++' so
$CC is a single executable, the probe passes, and Go uses a response
file.

Author: u9g

.github/workflows/session-e2e.yaml

@@ -68,19 +68,60 @@ jobs:
         with:
           version: 0.14.1
 
-      - name: Use Zig as cgo compiler (Windows)
-        if: matrix.os == 'windows-latest'
-        shell: bash
-        run: |
-          echo "CC=zig cc -target x86_64-windows-gnu" >> "$GITHUB_ENV"
-          echo "CXX=zig c++ -target x86_64-windows-gnu" >> "$GITHUB_ENV"
-
       - name: Set up Go
         uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c # v6
         with:
           go-version-file: go.mod
           cache: true
 
+      # Wrap `zig cc`/`zig c++` in single-binary launchers and point CC/CXX at
+      # them. Why not CC="zig cc -target ..." directly: the cgo build links ~560
+      # object files (webrtc APM + portaudio), whose paths overflow Windows'
+      # ~32KB command-line limit ("fork/exec zig.exe: The filename or extension
+      # is too long"). Go's linker avoids this by writing the args to a @response
+      # file, but only after probing that the linker accepts one -- and the probe
+      # runs only argv[0] of $CC. With a multi-token CC that's bare `zig` (no
+      # `cc` subcommand), so the probe fails, Go skips the response file, and the
+      # full argv overflows. A single-binary CC makes the probe pass. Must run
+      # after Set up Go (it builds the launchers) and before any cgo build.
+      - name: Build zig cgo launchers (Windows)
+        if: matrix.os == 'windows-latest'
+        shell: bash
+        run: |
+          dir="$(cygpath "$RUNNER_TEMP")/zigcc"
+          mkdir -p "$dir"
+          cat > "$dir/main.go" <<'EOF'
+          // Forwards to `zig cc`/`zig c++ -target x86_64-windows-gnu`, picking the
+          // subcommand from its own basename, so $CC/$CXX are single executables.
+          package main
+
+          import (
+          	"os"
+          	"os/exec"
+          	"path/filepath"
+          	"strings"
+          )
+
+          func main() {
+          	sub := "cc"
+          	if b := filepath.Base(os.Args[0]); strings.Contains(b, "xx") || strings.Contains(b, "++") {
+          		sub = "c++"
+          	}
+          	cmd := exec.Command("zig", append([]string{sub, "-target", "x86_64-windows-gnu"}, os.Args[1:]...)...)
+          	cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
+          	if err := cmd.Run(); err != nil {
+          		if ee, ok := err.(*exec.ExitError); ok {
+          			os.Exit(ee.ExitCode())
+          		}
+          		os.Exit(1)
+          	}
+          }
+          EOF
+          (cd "$dir" && go mod init zigcc && go build -o zcc.exe . && go build -o zxx.exe .)
+          win="$(cygpath -w "$dir")"
+          echo "CC=$win\\zcc.exe" >> "$GITHUB_ENV"
+          echo "CXX=$win\\zxx.exe" >> "$GITHUB_ENV"
+
       - name: Set up Python
         uses: actions/setup-python@v5
         with: