Rollup merge of rust-lang#68570 - cr1901:msp430-fix-1-2020, r=alexcri…

…chton

Bump LLVM submodule to fix LLVM assertion failure in MSP430 interrupt generation.

This PR brings in changes introduced by [this cherry-pick](rust-lang/llvm-project#37) to the Rust repository.

Nightlies downloaded from `rustup` do not appear to have llvm assertions enabled; the assertion failure [sometimes](YuhanLiin/msp430fr2355-quickstart#3) causes link errors that shouldn't occur. I couldn't find any indication of other bugs; however, it should still be fixed.