platform: arch linux support

* change shebang to python2
* use gcc-multilib on arch64, gcc on arch32
* x86_64 and os detection for arch with lsb_release and uname
* check if multilib repo is available
arch linux: support gtk and glib recipies
Arch: custom LDFLAGS for libkate
gobject-introspection: build with python2

use full path for python env in linux,
since shebangs are created from it in the build
fix cairo build with gcc 4.9