Nullability check for error module

Bugs: b/245972273
Test: adb shell
Change-Id: I9d1c20cf2a7e1e4201c3c54a321c9d9f896c92e2
diff --git a/libc/include/error.h b/libc/include/error.h
index 036a831..187ee17 100644
--- a/libc/include/error.h
+++ b/libc/include/error.h
@@ -44,7 +44,7 @@
  *
  * Available since API level 23.
  */
-extern void (*error_print_progname)(void) __INTRODUCED_IN(23);
+extern void (* _Nullable error_print_progname)(void) __INTRODUCED_IN(23);
 
 /**
  * [error_message_count(3)](http://man7.org/linux/man-pages/man3/error_message_count.3.html) is
@@ -70,7 +70,7 @@
  *
  * Available since API level 23.
  */
-void error(int __status, int __errno, const char* __fmt, ...) __printflike(3, 4) __INTRODUCED_IN(23);
+void error(int __status, int __errno, const char* _Nonnull __fmt, ...) __printflike(3, 4) __INTRODUCED_IN(23);
 
 /**
  * [error_at_line(3)](http://man7.org/linux/man-pages/man3/error_at_line.3.html) formats the given
@@ -80,6 +80,6 @@
  *
  * Available since API level 23.
  */
-void error_at_line(int __status, int __errno, const char* __filename, unsigned int __line_number, const char* __fmt, ...) __printflike(5, 6) __INTRODUCED_IN(23);
+void error_at_line(int __status, int __errno, const char* _Nonnull __filename, unsigned int __line_number, const char* _Nonnull __fmt, ...) __printflike(5, 6) __INTRODUCED_IN(23);
 
 __END_DECLS