libnativeloader: add a clarifying comment to Android.bp

Follow up to https://r.android.com/1136402

Bug: 137364733
Test: m nothing
Change-Id: Id78fd50d9f5e1a4cc9b17532c920f56033b7a45b
diff --git a/libnativeloader/Android.bp b/libnativeloader/Android.bp
index 2ee9d28..4b9c27f 100644
--- a/libnativeloader/Android.bp
+++ b/libnativeloader/Android.bp
@@ -89,6 +89,8 @@
         "libnativebridge-headers",
         "libnativeloader-headers",
     ],
+    // native_loader_test.cpp mocks libdl APIs so system_shared_libs
+    // are used to include C libraries without libdl.
     system_shared_libs: [
         "libc",
         "libm",