config: Add the iconv encodings to the defaults.
config: Control languages from the command line --with/--without options.

Allow a user to include languages by --with-objc or --without-cxx.
config: Support --without-rtems to not build RTEMS.

The default is to build RTEMS. This change lets a user stop this
by using '--without-rtems' on the command line.
config: Change to use the GCC POSIX thread model.
config: Add support for iconv encodings.

Turn off iconv support for the AVR because the arrays are too big.
doc: Add the patch module to cygwn.
doc: Add controlling the build. Add patch to cygwin.