Make android_get_application_target_sdk_version available to the NDK.

Also move this and android_get_device_api_level into <android/api-level.h>
so that they're always available.

This involves cleaning up <sys/cdefs.h> slightly.

Bug: N/A
Test: builds
Change-Id: I25435c55f3549cd0d827a7581bee75ea8228028b
diff --git a/libc/bionic/pthread_internal.cpp b/libc/bionic/pthread_internal.cpp
index 92786fe..2b7a99a 100644
--- a/libc/bionic/pthread_internal.cpp
+++ b/libc/bionic/pthread_internal.cpp
@@ -36,7 +36,6 @@
 #include <async_safe/log.h>
 
 #include "private/bionic_futex.h"
-#include "private/bionic_sdk_version.h"
 #include "private/bionic_tls.h"
 
 static pthread_internal_t* g_thread_list = nullptr;
@@ -114,7 +113,7 @@
   }
 
   // Historically we'd return null, but
-  if (bionic_get_application_target_sdk_version() >= __ANDROID_API_O__) {
+  if (android_get_application_target_sdk_version() >= __ANDROID_API_O__) {
     if (thread == nullptr) {
       // This seems to be a common mistake, and it's relatively harmless because
       // there will never be a valid thread at address 0, whereas other invalid