Replace llndk_library with llndk clause in cc_library

Remove the vestigial llndk_library and replace it with properties
in the llndk clause of the implementation cc_library.

In order to reduce duplication of the arch-specific headers used
by the implementation and LLNDK, rename libc_headers_arch to
libc_llndk_headers and hoist the "include" directory out of it,
since that directory is preproccessed separately for LLNDK
libraries.

Bug: 170784825
Test: m checkbuild
Test: compare out/soong/build.ninja
Change-Id: I75f0ff9129d910640da55eee6a6387467e6e4a9d
diff --git a/libm/Android.bp b/libm/Android.bp
index 10f794a..6c3abd1 100644
--- a/libm/Android.bp
+++ b/libm/Android.bp
@@ -26,7 +26,6 @@
     vendor_ramdisk_available: true,
     recovery_available: true,
     static_ndk_lib: true,
-    llndk_stubs: "libm.llndk",
 
     whole_static_libs: ["libarm-optimized-routines-math"],
 
@@ -528,6 +527,10 @@
         ],
     },
 
+    llndk: {
+        symbol_file: "libm.map.txt",
+    },
+
     apex_available: [
         "//apex_available:platform",
         "com.android.runtime",
@@ -544,12 +547,6 @@
     first_version: "9",
 }
 
-llndk_library {
-    name: "libm.llndk",
-    native_bridge_supported: true,
-    symbol_file: "libm.map.txt",
-}
-
 genrule {
     name: "libm.arm.map",
     out: ["libm.arm.map"],