Microsoft has added several new entries to the CV_CFL_LANG enum, including Rust: https://docs.microsoft.com/en-us/visualstudio/debugger/debug-interface-access/cv-cfl-lang This change adds Rust to the corresponding LLVM enum and translates `dwarf::DW_LANG_Rust` to `SourceLanguage::Rust` in the CodeView AsmPrinter. This means that Rust will no longer emit as Masm. Differential Revision: https://reviews.llvm.org/D115300