Merge GCC port updates

Merge GCC port updates

libposix changes
 * unimplemented methods do not abort, they warn instead
 * add pthread.h, no implementation yet
 * speed-up symbol redefinition (objcopy can work with static
   libraries as well)
 * add some functions already implemented in libc to libposix

toolchain changes
 * experimental support for HelenOS-specific toolchain
    * toolchain.sh --helenos-target
    * adds *-helenos*- target, e.g. we can have amd64-helenos-gcc
    * added as another choice to HelenOS.config, updated other scripts
      accordingly
 * added non-root compilation
   * install into PKG/ to be later copied to real root
     (package-like installation)