rust/.cargo/config

engine: 'if not, else' -> 'if, else'

I personally feel that

```
if x:
    pass
else:
    pass
```

is easier to read and edit than

```
if not x:
    pass
else:
    pass
```

Next patches will add one more if-else clause.

Differential Revision: https://phab.mercurial-scm.org/D9931

# 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"]