Support ARM compiler v6 for Keil

The PC-Lint Plus Configurator currently supports ARM compiler v5 for Keil. However, ARM v6 has been supported by Keil for some time, and so it would be useful if the Configurator did as well.

Note that ARM v6 is based on Clang, which is already supported by the Configurator for GCC installations. However, this doesn't set up the correct options for use with Keil. The options for Keil + ARM v5 seem to mostly (but not entirely) work with v6, but "official" support would be better.