Fix rustc sysroot in systems using CAS
Change filesearch::get_or_default_sysroot() to check if sysroot is found using env::args().next() if rustc in argv[0] is a symlink; otherwise, or if it is not found, use env::current_exe() to imply sysroot. This makes the rustc binary able to locate Rust libraries in systems using content-addressable storage (CAS).
Change filesearch::get_or_default_sysroot() to check if sysroot is found
using env::args().next() if rustc in argv[0] is a symlink; otherwise, or
if it is not found, use env::current_exe() to imply sysroot. This makes
the rustc binary able to locate Rust libraries in systems using
content-addressable storage (CAS).
In particular, this allows us to write more explicit matches that
avoid the pitfalls of using a fully general fall-through case, yet
remain fairly ergonomic. Less logic is in guard cases, more is in
the actual exhaustive case analysis.
No functional changes.
