Restrict the availability of the bionic libs

The bionic libs are now restricted to be in the runtime APEX and the
platform (for bootstrapping). It can still be referenced from other
APEXes but can't be included there.

Bug: 139870423
Test: m
Change-Id: I7f99eef27ccf75844ca5c9a7ea866496841b738f
diff --git a/libm/Android.bp b/libm/Android.bp
index 59466e4..b7bae54 100644
--- a/libm/Android.bp
+++ b/libm/Android.bp
@@ -501,6 +501,11 @@
         symbol_file: "libm.map.txt",
         versions: ["10000"],
     },
+
+    apex_available: [
+        "//apex_available:platform",
+        "com.android.runtime",
+    ],
 }
 
 ndk_library {