android: fix and test compilation to raw Android C code (#13080)

.github/workflows/ci_cross.yml

@@ -41,6 +41,11 @@ jobs:
           ./v -os windows cmd/v
           ./v -os windows examples/2048/2048.v
 
+      - name: Compile to raw Android (non-graphic) compatible
+        run: |
+          # Test that V can compile non-graphic app to Android compatible code *without* using the -apk flag
+          ./v -os android examples/toml.v
+
   linux-cross:
     runs-on: ubuntu-20.04
     timeout-minutes: 15
@@ -88,6 +93,12 @@ jobs:
           ./v -os windows examples/2048/2048.v
           ls -lart examples/2048/2048.exe
 
+      - name: toml.v can be compiled to raw Android C
+        run: |
+          # Test that V can compile non-graphic app to Android compatible code *without* using the -apk flag
+          ./v -os android examples/toml.v
+
+
   windows-cross:
     runs-on: windows-2019
     timeout-minutes: 15

vlib/os/os_android.c.v

@@ -19,6 +19,7 @@ fn C.AAsset_read(&C.AAsset, voidptr, int) int
 fn C.AAsset_close(&C.AAsset)
 
 pub fn read_apk_asset(file string) ?[]byte {
+	$if apk {
 		act := &C.ANativeActivity(C.sapp_android_get_native_activity())
 		if isnil(act) {
 			return error('Could not get reference to Android activity')
@@ -36,4 +37,7 @@ pub fn read_apk_asset(file string) ?[]byte {
 		}
 		C.AAsset_close(asset)
 		return buf
+	} $else {
+		return error(@FN + ' can only be used with APK/AAB packaged Android apps')
+	}
 }