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/wmi.h b/libc/kernel/uapi/linux/wmi.h
index 26f54d9..7b72056 100644
--- a/libc/kernel/uapi/linux/wmi.h
+++ b/libc/kernel/uapi/linux/wmi.h
@@ -30,17 +30,17 @@
   __u16 cmd_select;
   volatile __u32 input[4];
   volatile __u32 output[4];
-} __packed;
+} __attribute__((__packed__));
 struct dell_wmi_extensions {
   __u32 argattrib;
   __u32 blength;
   __u8 data[];
-} __packed;
+} __attribute__((__packed__));
 struct dell_wmi_smbios_buffer {
   __u64 length;
   struct calling_interface_buffer std;
   struct dell_wmi_extensions ext;
-} __packed;
+} __attribute__((__packed__));
 #define CLASS_TOKEN_READ 0
 #define CLASS_TOKEN_WRITE 1
 #define SELECT_TOKEN_STD 0