Add ARM Arch to the book

[William Harrington]

ARM needs to be added as an architecture for our build system.

Adding the book is not much different from a normal x86 build except that these few things need to be adjusted:

Kernel Headers GCC configure options

Kernel headers, either install the arm headers or download a kernel specific for any platform ( aka Raspberry pi)

GCC, adjust options for cpu, float, and vfpu, and possibly something else.

We need a table for various ARM cpu's with the options to use with GCC during configure regarding float, vfp, and target triplet.

We'll have a table for targets like with mips.

Any input will be great for starting a table with the proper options and can update GCC with some variables to use during configure from the table regarding target triplet, cpu, vfp, and float info.

[William Harrington]

Aaediwen and I have been working with Raspberry PI 3 builds. It won't take much work to add ARM to the book. It's an x86 book with arm changes. However, with AARCH64 coming out, it would complicate the addition a bit more. For now, I suggest just dealing with ARMv7 and less.

[William Harrington]

Just a simple example of a Raspberry Pi3 build using Raspbian and current CLFS Dev:

Kernel Headers Install

ARCH=arm

GCC:

--with-cpu=cortex-a53     --with-fpu=neon-fp-armv8     --with-float=hard

That's about all I can remember right now.