CCCSP subtarget support; adjusted option handling.

This adds some changes that make CCCSP "subtarget" aware, experimenting with generating Guppy code for the EV3.  Subtarget choice influences the way NOCC finds and instantiates the C compiler in the CCCSP back-end, bit hacky but needed to handle using the cross-compiler without busting normal operation (and allowing generated libraries/etc. to co-exist).  Fiddled the global option handling so that some specs-file things are only set if *not* given on the command-line (i.e. command-line will override specs-file).