pkg/libuv: generate cimport.zig for specific platforms

pkg/libuv/c.zig

@@ -7,5 +7,13 @@ pub usingnamespace switch (builtin.zig_backend) {
 
     // Workaround for:
     // https://github.com/ziglang/zig/issues/12325
-    else => @import("cimport.zig"),
+    //
+    // Generated by:
+    // zig translate-c -target aarch64-macos -lc -Ivendor/libuv/include vendor/libuv/include/uv.h
+    // (and then manually modified)
+    else => switch (builtin.os.tag) {
+        .macos => @import("cimport_macos.zig"),
+        .linux => @import("cimport_linux.zig"),
+        else => @compileError("unsupported OS for now, see this line"),
+    },
 };