Provide an option for the base/rom extension that causes the toolchain id (ARMCC or GCCE) to be defined for the C preprocessor phase of rombuild, enabling rom files to be conditionally included or excluded depending on whether the toolchain can build them. This mimics the same change for Beagleboard.

[SERIALCOMM]
PDD EUART1
LDD ECOMM
CSY ECUART
PORT 1
RATE 115200