ffi 1.14: #objc_call OS-gating cross-compiles cleanly to Android

109/109 host tests pass; tests/cross_compile.sh's first real tuple
(`android | examples/ffi-objc-call-10-os-gate.sx`) compiles
through `sx build --target android` without finding any
`@objc_msgSend` / `@sel_registerName` symbols in the output —
the `inline if OS == .ios { #objc_call(...) }` arm is stripped
at sx compile time before emit_llvm runs, so the Android
toolchain (Bionic + libGLESv3 / NDK linker) doesn't see the
Obj-C runtime references that would otherwise be undefined.

Host (macOS): the example prints "host stripped both" — the iOS
arm is stripped (we're not iOS) AND the Android arm is stripped
(we're not Android), confirming `inline if OS == { case }`
symmetric strip-and-render works around `#objc_call` sites.

The example carries a 3-line `android_main` trampoline so the
NDK linker's `-u ANativeActivity_onCreate` / entry-point
discovery is satisfied — pattern shared with chess + the other
android examples.

tests/cross_compile.sh

@@ -22,9 +22,12 @@ TMP_DIR="${TMPDIR:-/tmp}/sx-cross-compile"
 mkdir -p "$TMP_DIR"
 
 # Tuple format: "<target>|<example_path>"
-# Add entries as cross-only examples land. Empty for now — Phase 0 only
-# lays down the runner; baselines live in tests/run_examples.sh territory.
-TUPLES=()
+# Add entries as cross-only examples land. Verifies the example
+# compiles cleanly for the target's NDK / SDK without needing the
+# host to actually run it.
+TUPLES=(
+    "android|examples/ffi-objc-call-10-os-gate.sx"
+)
 
 PASS=0
 FAIL=0

tests/expected/ffi-objc-call-10-os-gate.exit

@@ -0,0 +1 @@
+0

tests/expected/ffi-objc-call-10-os-gate.txt

@@ -0,0 +1 @@
+host stripped both