Add linux headers 5.10.41.

Needed for kexec-tools.

Not equivalent to kernel version; kernel API is stable and does not
change. Therefore we can use any (latest) version.

sysa/linux-headers-5.10.41/linux-headers-5.10.41.sh

@@ -0,0 +1,62 @@
+# SPDX-FileCopyrightText: 2021 fosslinux <fosslinux@aussies.space>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+src_unpack() {
+    src_dir="${base_dir}/src"
+    tar -xzf "${src_dir}/"*.tar.gz "${dirname}/scripts"
+    tar -xzf "${src_dir}/"*.tar.gz "${dirname}/include"
+    tar -xzf "${src_dir}/"*.tar.gz "${dirname}/arch/x86/include"
+    tar -xzf "${src_dir}/"*.tar.gz "${dirname}/arch/x86/entry"
+}
+
+src_prepare() {
+    default
+
+    # Buggy headers/don't know how to account for
+    rm include/uapi/linux/pktcdvd.h \
+        include/uapi/linux/hw_breakpoint.h \
+        include/uapi/linux/eventpoll.h \
+        include/uapi/linux/atmdev.h \
+        include/uapi/asm-generic/fcntl.h \
+        arch/x86/include/uapi/asm/mman.h \
+        arch/x86/include/uapi/asm/auxvec.h
+}
+
+src_compile() {
+    gcc -o scripts/unifdef scripts/unifdef.c
+}
+
+src_install() {
+    export base_dir="${PWD}"
+    # We "compile" the headers here because it is easier
+    for d in include/uapi arch/x86/include/uapi; do
+        cd "${d}"
+        find . -type d -exec mkdir "/after/include/{}" -p \;
+        headers="$(find . -type f -name "*.h")"
+        cd "${base_dir}"
+        for h in ${headers}; do
+            scripts/headers_install.sh "${d}/${h}" "/after/include/${h}"
+        done
+    done
+
+    # Pick-and-choose asm-generic headers
+    cp /after/include/asm-generic/types.h /after/include/asm/types.h
+    cp /after/include/asm-generic/ioctl.h /after/include/asm/ioctl.h
+
+    # Generate asm/unistd_32.h
+    bash arch/x86/entry/syscalls/syscallhdr.sh \
+        arch/x86/entry/syscalls/syscall_32.tbl \
+        /after/include/asm/unistd_32.h i386
+
+    # Generate linux/version.h
+    # Rules are from makefile
+    VERSION=5
+    PATCHLEVEL=10
+    SUBLEVEL=42
+    VERSION_CODE="$((${VERSION} * 65536 + ${PATCHLEVEL} * 256 + ${SUBLEVEL}))"
+    echo '#define LINUX_VERSION_CODE '"${VERSION_CODE}" \
+        > /after/include/linux/version.h
+    echo '#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + ((c) > 255 ? 255 : (c)))' \
+        >> /after/include/linux/version.h
+}