Make the connection between implementation and llndk_library explicit

Instead of assuming a module with the .llndk suffix exists, add an
llndk_stubs property to every cc_library module that has a
corresponding llndk_library.  Also rename the llndk_library to have
an explicit .llndk suffix.

Bug: 170784825
Test: no changes to build.ninja (excluding comments) or Android-${TARGET_PRODUCT}.mk
Change-Id: Ib5453472a09ebc64818ceb69bcbe1184720ce86a
diff --git a/libm/Android.bp b/libm/Android.bp
index 7f96975..50244d9 100644
--- a/libm/Android.bp
+++ b/libm/Android.bp
@@ -7,6 +7,7 @@
     ramdisk_available: true,
     recovery_available: true,
     static_ndk_lib: true,
+    llndk_stubs: "libm.llndk",
 
     whole_static_libs: ["libarm-optimized-routines-math"],
 
@@ -520,7 +521,7 @@
 }
 
 llndk_library {
-    name: "libm",
+    name: "libm.llndk",
     native_bridge_supported: true,
     symbol_file: "libm.map.txt",
 }