android : use release cmake build type by default (#5123)

examples/llama.android/app/build.gradle.kts

@@ -30,6 +30,7 @@ android {
         }
         externalNativeBuild {
             cmake {
+                arguments += "-DCMAKE_BUILD_TYPE=Release"
                 cppFlags += listOf()
                 arguments += listOf()
             }