Create a soong module for ndk_system STL headers

This STL does not have a prebuilt, but does provide headers for
compilation. Soong adds -isystem
prebuilts/ndk/current/sources/cxx-stl/system/include to the compile path
for modules that have stl = "ndk_system"

Bazel poses stricter sandboxing constraints. In preparation for
building sdk variants with Bazel, create a Soong module that explicitly
specifies the .h files contributed by this STL (via
export_system_include_dirs).

This will be a no-op in Soong.

Test: m nothing
Bug: 298258442
Change-Id: If40b644fdaf23dc99a563a7265e9e4b38f8626ef
diff --git a/Android.bp b/Android.bp
index 9b8550e..3c22867 100644
--- a/Android.bp
+++ b/Android.bp
@@ -75,3 +75,18 @@
     sdk_version: "minimum",
     export_include_dirs: ["current/sources/android/cpufeatures"],
 }
+
+// A module that encapsulates the header files of NDK System STL
+cc_library_headers {
+    name: "ndk_system",
+    sdk_version: "minimum",
+    sdk_variant_only: true,
+    stl: "none",
+    export_system_include_dirs: ["current/sources/cxx-stl/system/include"],
+    // the headers are available to both the platform and anyapex.
+    // this availability is required to compile jni deps of any android_app in these api domains.
+    apex_available: [
+        "//apex_available:anyapex",
+        "//apex_available:platform",
+    ],
+}