MSP430G2553 WDT ISR compilation error - GNU v4.9.1
I'm taking a wild guess here, but maybe you've accidentally enabled Large Memory Model (on newer MSP430s it allows you to address up to 1MB of memory), which turns function pointers to 32-bit, so the pointer to your WDT_ISR() overflows the interrupt vector by two bytes. Check if you're passing the correct compiler flags to GCC.