Define __INTRODUCED_IN_LLNDK

Symbols with __INTRODUCED_IN_LLNDK are available for LLNDK only if
the vendor api level set by the RELEASE_BOARD_API_LEVEL is equal to
or newer than the target vendor api level in __INTRODUCED_IN_LLNDK.

This works only for the vendor variants at the same time ignoring
__INTRODUCED_IN annotation for the vendor variants. On the other
hand, __INTRODUCED_IN_LLNDK will be ignored from non-vendor variants.

Bug: 302113279
Test: build
Change-Id: I5317a73dbc73095f8d5d95131ca4d9ed39df6be1

libvendorsupport/Android.bp

@@ -34,3 +34,21 @@ cc_library {
         "liblog",
     ],
 }
+
+cc_library_headers {
+    name: "libvendorsupport_llndk_headers",
+    host_supported: true,
+    vendor_available: true,
+    recovery_available: true,
+    ramdisk_available: true,
+    vendor_ramdisk_available: true,
+    native_bridge_supported: true,
+
+    export_include_dirs: ["include_llndk"],
+    llndk: {
+        llndk_headers: true,
+    },
+
+    system_shared_libs: [],
+    stl: "none",
+}

libvendorsupport/include_llndk/android/llndk-versioning.h

@@ -0,0 +1,48 @@
+// Copyright (C) 2024 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+#if defined(__ANDROID_VENDOR__)
+
+// LLNDK (https://source.android.com/docs/core/architecture/vndk/build-system#ll-ndk) is similar to
+// NDK, but uses its own versioning of YYYYMM format for vendor builds. The LLNDK symbols are
+// enabled when the vendor api level is equal to or newer than the ro.board.api_level.
+#define __INTRODUCED_IN_LLNDK(vendor_api_level)                                             \
+    _Pragma("clang diagnostic push") _Pragma("clang diagnostic ignored \"-Wgcc-compat\"")   \
+            __attribute__((enable_if(                                                       \
+                    __ANDROID_VENDOR_API__ >= vendor_api_level,                             \
+                    "available in vendor API level " #vendor_api_level " that "             \
+                    "is newer than the current vendor API level. Guard the API "            \
+                    "call with '#if (__ANDROID_VENDOR_API__ >= " #vendor_api_level ")'."))) \
+            _Pragma("clang diagnostic pop")
+
+// For the vendor libraries, __INTRODUCED_IN must be ignored because they are only for NDKs but not
+// for LLNDKs.
+#undef __INTRODUCED_IN
+#define __INTRODUCED_IN(x)
+
+#else  // __ANDROID_VENDOR__
+
+// For non-vendor libraries, __INTRODUCED_IN_LLNDK must be ignored because it must not change
+// symbols of NDK or the system side of the treble boundary.
+#define __INTRODUCED_IN_LLNDK(vendor_api_level)
+
+#endif  // __ANDROID_VENDOR__
+
+__END_DECLS