clippy-driver: if --sysroot is specified on the command line, use that
clippy-driver: if --sysroot is specified on the command line, use that

If the user explicitly sets sysroot on the command line, then use that
value.

Issue #3663

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