* msp430/crt0.S (high_bss): Add.
* msp430/msp430-sim.ld: Add error message if .upper sections are
detected.
* msp430/msp430xl-sim.ld (MEMORY): Adjust to better mimic real
life MCUs. Add support for upper and lower sections.
from crt0.S with -DMINRT.
(CRT_OBJS): Expand.
(crt_%.o): New rule pattern. Build multiple objects from crt0.S.
* msp430/crt0.S: Further break out functionality. Support -DMINRT
that omits all init/fini logic.
* msp430/crtn.S: Likewise.
* msp430/msp430-sim.ld: Wildcard all .crt_* sections, sorted.
* msp430/msp430.ld: Likewise.
* msp430/msp430xl-sim.ld: Likewise.