Add and use constants for the Android API levels.

Test: bionic tests still pass
Change-Id: If1b619cfc9db1d3f5d91f14f2ace71058dca0c4a
diff --git a/tests/dlext_test.cpp b/tests/dlext_test.cpp
index 8527b00..ed50ea5 100644
--- a/tests/dlext_test.cpp
+++ b/tests/dlext_test.cpp
@@ -1191,10 +1191,9 @@
 }
 
 TEST(dlext, dlopen_handle_value_app_compat) {
-  android_set_application_target_sdk_version(23);
+  android_set_application_target_sdk_version(__ANDROID_API_M__);
   void* handle = dlopen("libtest_dlsym_from_this.so", RTLD_NOW | RTLD_LOCAL);
   ASSERT_TRUE(reinterpret_cast<uintptr_t>(handle) % sizeof(uintptr_t) == 0)
           << "dlopen should return valid pointer";
   dlclose(handle);
 }
-