Support building libjnigraphics on the host

Bug: 169137236
Test: SANITIZE_HOST=address make imagedecoder_fuzzer

Along with a change in frameworks/base
(I0ffc4e90b4083db79fbb12012e2e1284206b43e3), this will make it possible
to run imagedecoder_fuzzer on the host, for faster fuzzing.

imagedecoder.h:
- define __ANDROID_API__ and __INTRODUCED_IN on non-Android systems, so
  methods can be called on those systems.

bitmap.h:
- define __ANDROID_API__ and __INTRODUCED_IN on non-Android systems, so
  methods can be called on those systems.
- include <stddef.h>, which is needed on non-Android systems for size_t.
- on Android, unguard types and enums for easier opportunistic usage via
  dlsym.

nativewindow/Android.bp
- make libnativewindow_headers host_supported, so that libjnigraphics
  can access android/data_space.h

Change-Id: Iefdb4132d6f10f9164be85f4dc6e11883f6fd37e
diff --git a/include/android/imagedecoder.h b/include/android/imagedecoder.h
index 6fcc9b9..fcc0b9b 100644
--- a/include/android/imagedecoder.h
+++ b/include/android/imagedecoder.h
@@ -51,6 +51,20 @@
 #include <android/rect.h>
 #include <stdint.h>
 
+#ifndef __ANDROID__
+    // Value copied from 'bionic/libc/include/android/api-level.h' which is not available on
+    // non Android systems. It is set to 10000 which is same as __ANDROID_API_FUTURE__ value.
+    #ifndef __ANDROID_API__
+        #define __ANDROID_API__ 10000
+    #endif
+
+    // Value copied from 'bionic/libc/include/android/versioning.h' which is not available on
+    // non Android systems
+    #ifndef __INTRODUCED_IN
+        #define __INTRODUCED_IN(api_level)
+    #endif
+#endif
+
 #ifdef __cplusplus
 extern "C" {
 #endif