Merge GCC port updates

Merge GCC port updates

This commit includes various small changes needed to compile GCC or
dependent libraries on more architectures than ia32.

A lot of ARM EABI functions (softfloat) were added, mostly as aliases
to already existing ones.

A generic implementation of long jump was added, based on context save
and restore functions.

Examples in src/c/ were updated to be compilable again and new scripts
for compiling with GCC were added.

New uspace/overlay directory was added that is verbatim copied into the
final image. Cleaning its content is left to the user.

A small `untar' utility was implemented for unpacking tarballs (it does
not support the standard switches nor a compressed content).

Merged branch: lp:~vojtech-horky/helenos/gcc-port