[GWP-ASan] Change sys/cdefs.h to features.h

sys/cdefs.h is a glibc internal header which is not supposed to be included by applications.
(Some libc implementations provide this file for compatibility.)
Android features.h includes sys/cdefs.h, so we can include features.h instead.

This change makes `ninja gwp_asan` build on musl.

Author: MaskRay

compiler-rt/lib/gwp_asan/platform_specific/utilities_posix.cpp

@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <sys/cdefs.h> // IWYU pragma: keep (for __BIONIC__ macro)
+#include <features.h> // IWYU pragma: keep (for __BIONIC__ macro)
 
 #ifdef __BIONIC__
 #include "gwp_asan/definitions.h"