One-line addition to the `call_method_offset` switch in
`emit_llvm.zig` — `.s32 => 49` (CallIntMethod). The 1.17 caching
infrastructure handles the rest: GetObjectClass → NewGlobalRef →
GetMethodID populate the shared `@SX_JNI_{CLS,MID}_<key>` pair on
miss; per-call lowering loads the cached jmethodID and dispatches
through vtable slot 49 with an `i32` return.
IR snapshot at `tests/expected/ffi-jni-call-04-jint-return.ir`
updated: the `ret i32 undef` placeholder is replaced by the full
lazy-cache + CallIntMethod sequence keyed on
`("getCount", "()I")`. Pre-1.18 snapshot was 1d7ea72.
Adds `examples/ffi-jni-call-04-jint-return.sx` exercising
`#jni_call(s32)(env, target, "getCount", "()I")` inside a runtime-
reachable but never-invoked helper (`g_should_call` stays false, so
the dereferences don't fire). Today the emit_llvm switch falls
through to `LLVMGetUndef` for any non-void return — the IR snapshot
captures that placeholder.
The next commit adds the `.s32 => 49` (CallIntMethod) arm. The
snapshot will update to show the full GetObjectClass → GetMethodID →
CallIntMethod sequence (reusing the slot interning landed in 1.17,
since `("getCount", "()I")` is a fresh literal pair).
