rust-status: add trace-level logging for Rust status fallback for debugging
The added `log` crate is already a sub-dependency.
Differential Revision: https://phab.mercurial-scm.org/D8300
# Rust builds with a modern MSVC and uses a newer CRT.
# Python 2.7 has a shared library dependency on an older CRT (msvcr90.dll).
# We statically link the modern CRT to avoid multiple msvcr*.dll libraries
# being loaded and Python possibly picking up symbols from the newer runtime
# (which would be loaded first).
[target.'cfg(target_os = "windows")']
rustflags = ["-Ctarget-feature=+crt-static"]