Difference between `gcc` and `gcc-msp430`
gcc (alone) is your local machine compiler that generates code for x86 and x86-64 (ie. the target is your computer, unless you are running on non-x86). gcc-msp430 is the cross compiler that runs on your computer, but generates machine code for MSP430.

Generally one GCC installation supports a single target (ie. family of CPUs having the same or very close ISA), like x86, ARM or AVR. For example the MSP430 flavor will support arguments like msp430g2553, while ARM flavor will support cortex-m3. A compiler triplet is used to fully identify the compiler.

Each of the targets also has its own options. Your can find them here.