Replace __packed with __attribute__((__packed__)) in uapi headers

Linux uapi headers use __packed as an abbreviation for
__attribute__((__packed__)).  In the upstream kernel headers this
is defined in linux/compiler_attributes.h, but it is not defined
in the uapi headers.  Bionic defines it in sys/cdefs.h, which will
almost always provide the needed definition, but there are uapi
headers that use __packed and do not include any system headers
that would include sys/cdefs.h.  Musl's sys/cdefs.h does not
define __packed, which leads to linker errors when __packed is
treated as a variable name.

Replace __packed with __attribute__((__packed__)) when importing
uapi headers to break the dependency on sys/cdefs.h.

Test: m USE_HOST_MUSL=true on oriole-userdebug in internal master
Change-Id: I45f80f4e5aec868b80ce8eb9d757a3e08ae3e1a9
diff --git a/libc/kernel/uapi/linux/android/binder.h b/libc/kernel/uapi/linux/android/binder.h
index e3b3289..52f4c6b 100644
--- a/libc/kernel/uapi/linux/android/binder.h
+++ b/libc/kernel/uapi/linux/android/binder.h
@@ -189,7 +189,7 @@
 struct binder_handle_cookie {
   __u32 handle;
   binder_uintptr_t cookie;
-} __packed;
+} __attribute__((__packed__));
 struct binder_pri_desc {
   __s32 priority;
   __u32 desc;