ffi #jni_main R.2: drop native_app_glue from Android link when #jni_main present

`target.link` now takes a `has_jni_main: bool` parameter (passed by
main.zig from `comp.getJniMainEmissions().len > 0`). When set:

  - native_app_glue.c is not compiled — no `.glue.o` produced.
  - `-u ANativeActivity_onCreate` is not added to the link argv.
  - The Java-driven Activity is the entry; the .so just provides JNI
    impls, bound at load time via the `JNI_OnLoad` slice R.3 will
    synthesize.

Legacy NativeActivity builds (no `#jni_main` decl) are unchanged: glue
is still compiled and `ANativeActivity_onCreate` still retained.

Verified end-to-end:
  - #jni_main .so: `llvm-nm -D` shows neither `ANativeActivity_onCreate`
    nor `android_main` (correct — Java side drives entry).
  - Legacy .so (99-android-egl-clear): both symbols still exported.

131 host / 4 cross / zig build test all green.

src/main.zig

@@ -595,7 +595,7 @@ fn compileWithTimer(allocator: std.mem.Allocator, io: std.Io, input_path: []cons
 
     // Link (sx .o + C .o files)
     timer.mark();
-    sx.target.link(allocator, io, obj_path, c_obj_paths, final_output, libs, fws, merged_config) catch {
+    sx.target.link(allocator, io, obj_path, c_obj_paths, final_output, libs, fws, merged_config, comp.getJniMainEmissions().len > 0) catch {
         std.debug.print("error: linking failed\n", .{});
         return error.CompileError;
     };