multilib_header_wrapper.h: Use #pragma once

Avoid infinite include loops, especially with bits/wordsize.h which is
now possible with the synthesized headers since we now also synthesize
bits/wordsize.h itelf for some arches e.g. arm/aarch64

In cases where extra preprocessing tools are used such as clang-tidy
e.g. and these tools are not passed the knowledge about architecture
then case comes where we enter into header include loop for
bits/wordsize.h, since this template does explicitly include
bits/wordsize.h

To fix this emits the pragma once at beginning of file, this is better
solution than include guards, and pragma once is practically supported
on all compilers except few e.g. cray c/c++ compiler

(From OE-Core rev: 6ab11ac25bb987642d5ca1a07f4bd5f30c66c9c5)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/multilib_header_wrapper.h

@@ -21,6 +21,7 @@
  * 
  */
 
+#pragma once
 
 #if defined (__bpf__)
 #define __MHWORDSIZE			64