uapi: wrap compiler_types.h in an ifdef instead of the implicit strip

The uAPI stddef header includes compiler_types.h, a kernel-only
header, to make sure that kernel definitions of annotations
like __counted_by() take precedence.

There is a hack in scripts/headers_install.sh which strips includes
of compiler.h and compiler_types.h when installing uAPI headers.
While explicit handling makes sense for compiler.h, which is included
all over the uAPI, compiler_types.h is only included by stddef.h
(within the uAPI, obviously it's included in kernel code a lot).

Remove the stripping from scripts/headers_install.sh and wrap
the include of compiler_types.h in #ifdef __KERNEL__ instead.
This should be equivalent functionally, but is easier to understand
to a casual reader of the code. It also makes it easier to work
with kernel headers directly from under tools/

Signed-off-by: Jakub Kicinski <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

include/uapi/linux/stddef.h

···
 #ifndef _UAPI_LINUX_STDDEF_H
 #define _UAPI_LINUX_STDDEF_H
 
+#ifdef __KERNEL__
 #include <linux/compiler_types.h>
+#endif
 
 #ifndef __always_inline
 #define __always_inline inline

scripts/headers_install.sh

···
 sed -E -e '
 	s/([[:space:](])(__user|__force|__iomem)[[:space:]]/\1/g
 	s/__attribute_const__([[:space:]]|$)/\1/g
-	s@^#include <linux/compiler(|_types).h>@@
+	s@^#include <linux/compiler.h>@@
 	s/(^|[^a-zA-Z0-9])__packed([^a-zA-Z0-9_]|$)/\1__attribute__((packed))\2/g
 	s/(^|[[:space:](])(inline|asm|volatile)([[:space:](]|$)/\1__\2__\3/g
 	s@#(ifndef|define|endif[[:space:]]*/[*])[[:space:]]*_UAPI@#\1 @