clippy-driver: fix test and add --rustc to --help output

.github/driver.sh

@@ -31,9 +31,11 @@ diff normalized.stderr tests/ui/cstring.stderr
 SYSROOT=`rustc --print sysroot`
 diff <(LD_LIBRARY_PATH=${SYSROOT}/lib ./target/debug/clippy-driver --rustc --version --verbose) <(rustc --version --verbose)
 
+
+echo "fn main() {}" > target/driver_test.rs
 # we can't run 2 rustcs on the same file at the same time
-CLIPPY=`LD_LIBRARY_PATH=${SYSROOT}/lib ./target/debug/clippy-driver tests/driver/main.rs`
-RUSTC=`rustc tests/driver/main.rs`
+CLIPPY=`LD_LIBRARY_PATH=${SYSROOT}/lib ./target/debug/clippy-driver ./target/driver_test.rs --rustc`
+RUSTC=`rustc ./target/driver_test.rs`
 diff <($CLIPPY) <($RUSTC)
 
 # TODO: CLIPPY_CONF_DIR / CARGO_MANIFEST_DIR

src/driver.rs

@@ -207,6 +207,7 @@ Usage:
 
 Common options:
     -h, --help               Print this message
+        --rustc              Pass all args to rustc
     -V, --version            Print version info and exit
 
 Other options are the same as `cargo check`.