ANN: GCC 7.1.0 for arm-eabi

[Simon Wright <simon@pushface.org>]

GCC 7.1.0, rebuilt as a cross-compiler from macOS to arm-eabi, is
available at
https://sourceforge.net/projects/gnuada/files/GNAT_GCC%20Mac%20OS%20X/7.1.0/arm-eabi/

The compiler is known to run on El Capitan and Sierra; it may not run
on earlier OS X releases.

The compiler was tested with the Cortex-M3 as found on the Arduino
Due[1] and the Cortex-M4 as found on the STMicroelectronics[2] STM32F4
Discovery and STM32F429I Discovery boards. Note, however, that GCC 7 has
implemented multilib support for other ARM chips.

GNAT GDB 2016 (rebuilt for arm-eabi) is included.

The compiler comes with no Ada Runtime System (RTS). See the Cortex GNAT
Run Time Systems project[3] for candidates.

NOTE 1: the compiler/RTS interface has changed; for the time being, you
will need to check out the latest repository update.

NOTE 2: for the same reason, this compiler can't presently be used with
AdaCore's embedded-runtimes repository at Github[4].

[1] http://www.arduino.com
[2] http://www.st.com
[3] https://sourceforge.net/projects/cortex-gnat-rts/
[4] https://github.com/AdaCore/embedded-runtimes