#5 Add multilibs for ARM and Thumb +/- interworking

[Greg Parker]

This patch makes prc-tools build four sets of libraries for arm-
palmos: ARM-only, Thumb-only, ARM interworked, and Thumb
interworked.

Currently, prc-tools 2.3 just builds ARM-only and Thumb-only
libgcc, and ARM-only libc.

The patch to libc/Makefile.in isn't the best, but I couldn't figure
out a way to generalize the mown-gp machinery already in
place.

[Greg Parker]

multilib.patch