sabotage's linux kernel headers

linux headers are often broken for userspace, and downloading the entire kernel tarball just to get the headers is overkill.

thus we provide our own copy for the archs supported by sabotage.

some minor issues are fixed, plus libc-compat.h is patched to offer the same level of support for musl libc as the vanilla headers offer for glibc.

we currently use the headers of kernel 4.19.88, which is a recent long-term-support kernel. There are previous 4.4.2, 3.3.4, and 3.12.6 branches.

Installation:

make ARCH=xxx prefix=/usr DESTDIR=/opt/package install

where ARCH is the name of one of the arch-specific directories. for example, i386, x86_64, x32, powerpc, mips, microblaze.

Download mirrors for release tarballs:

• DE : http://ftp.barfooze.de/pub/sabotage/tarballs/
• GR : http://foss.aueb.gr/mirrors/linux/sabotage/tarballs/
• UK : http://dl.2f30.org/mirrors/sabotage/tarballs/

Adding a new arch:

export ARCH=xxx
tar xf linux-4.4.2.tar.xz && cd linux-4.4.2
CC=false make V=1 ARCH=$ARCH INSTALL_HDR_PATH=dest headers_install
rm dest/include/asm/.*install*
cd ..
cp -r sh $ARCH
rm -rf $ARCH/include/asm
cp -r linux-4.4.2/dest/include/asm $ARCH/include
rm -rf linux-4.4.2