archlinux-seckernel: update PKGBUILD patch
c_examples: improve cpuid
gitignore: ignore every compiled files in c_examples
nolibc: use xchg instead of push/pop for x86 PIC

GCC uses such construct, for example in libgomp:
    libgomp/config/linux/x86/futex.h
c_examples: add OpenMP example with matrix computation
Add a global Makefile which calls every other Makefiles
Simplify the global Makefile