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/

JKJakub Kicinski committed 1 year ago