* config/msp430/msp430.md (movsi_s): New.  Special case for
storing a 20-bit symbol into a 32-bit register.
* config/msp430/msp430.c (msp430_subreg): Add support for it.
* config/msp430/predicates.md (msp430_symbol_operand): New.

From-SVN: r224145