Instruct lld that our @ files are posix-style, not Windows
Instruct lld that our @ files are posix-style, not Windows

An upstream LLVM change changed behavior here to respect the host system quoting
rules; previously the posix-style format was always used for @files.

graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust