Build: Add architecture rule for libshared.a.

- As suggested by Ingo, add libshared.a to the architecture name map.
This allows it to be linked by its short name like other frequently
used libraries.
- Adjust all Jamfiles referencing the lib accordingly.

<disk_system>fat: fix gcc4 build

I noticed the syntax for libsupc++ in the BFS Jamfile addon differed but didn't think it mattered.

Add FAT addon for DriveSetup

Tested with a 5MB image, seems to work.

There seems to be an issue with too long names though, or possibly names with spaces.

Also, technically it supports FAT12,16 and 32, so it should probably be renamed
in the interface.

Didn't check how to declare support for more than 1 partition types either.