new port: msp430-elf

[DJ Delorie]

The assembler already exists (and is widely used, I think), and the
MSPABI specifies how registers and symbols are named at the assembler
level.  Unfortunately, the MSPABI says that symbols should be like
||this|| when they need to mean "not a register" but our assembler
doesn't support that.  The mspgcc gcc uses underscores on symbols that
are register names, but that just moves the problem.  I could also
look into using +this to handle some cases, but I'd have to look into
how the assembler parses things.

So, it's not that I don't have *a* solution, it's that I have a
*couple* of solutions, and I'm not sure which is the one worth
persuing just yet.  Hence, release notes.