Add preliminary support for inline assembly for msp430.
The `llvm_asm` macro was removed recently, and the MSP430 backend relies on inline assembly to build useful embedded apps. I conveniently "found" time to implement basic support for the new inline `asm` macro syntax with the help of `@Amanieu` :D.
In addition to tests in the compiler, I have tested this locally against deployed MSP430 code and have not found any noticeable differences in firmware operation or `objdump` disassemblies between the old `llvm_asm` and the new `asm` syntax.
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