Add support for the NXP Freedom-K64F board.  This is primarily the work of Jordan Macintyre.  I leveraged this code from https://github.com/jmacintyre/nuttx-k64f

*  This driver supports the 'I2C lcd backpack' design that is based on the PCF8574 io expander.  There's a myriad of different vendors of such, but they are principally the same, save wiring and minor features like jumpers for I2C addresses.  This driver supports known and unknown variants.
*  The interface board supports HD44780-based LCD modules up to 4x32, and this driver accommodates all those formats.

configs/nucleus2g:  Remove this board from the configs/ directory.  A snapshot is still available in the Obsoleted repository

Signals:  Correct implementation of sigset().  It is not just signal() with a different name; it has some additional signal mask handling functionality

Optional canned symtab inclusion to the build. When option CONFIG_LIBC_SYMTAB is selected and symbol table file libc/symtab/canned_symtab.inc is prepared then application can use system provided complete symbol table. The option has substantial effect on system image size. Mainly code/text. If loading of applications at runtime is not planned do not select this.  From Pavel Pisa.