Use correct gzcat tool where it is available.

Pure zcat tends to fail on the "difficult" Unices.
Use gtar tool where it is available.

Regular tar tends to fail on Solaris.
Don't let the POSIX shell test output anything.

It interferes with scripts that we need to run without producing any
output.
Include functions script in order to get a compliant shell on Solaris.
Delete bogus file created by tar before comparison.
Use rsync instead of cp, since GNU and AIX cp are incompatible.
Remove redundant specification of package file.
Remove useless AIX specific section.

They apparently tried to solve some problem on AIX, but all they did
was make it harder to build.

Also introduce one AIX specific flag that we *do* need, since the ELF
way of building libraries (.so files) is not the default there.
Make libgcc build script less sensitive to gcc version.

Also remove libstdc++ from the package, which no dependee actually
uses.
Merge pull request #11 from kacfengine/build_fixes

Build fixes