Sightglass CLI: allow hyphens in engine flags.

Currently, `--engine-flags '-Ccranelift-...=...'` fails to work because
the structopt argument parser sees the `-C...` as a new argument. The
`allow_hyphen_values` option allows such usage to work, which is very
convenient for running experiments with different optimization options
without rebuilding the `.so` with modified defaults.

Author: cfallin

crates/cli/src/benchmark.rs

@@ -50,7 +50,11 @@ pub struct BenchmarkCommand {
 
     /// Configure an engine using engine-specific flags. (For the Wasmtime
     /// engine, these can be a subset of flags from `wasmtime run --help`).
-    #[structopt(long("engine-flags"), value_name = "ENGINE_FLAGS")]
+    #[structopt(
+        long("engine-flags"),
+        value_name = "ENGINE_FLAGS",
+        allow_hyphen_values = true
+    )]
     engine_flags: Option<String>,
 
     /// How many processes should we use for each Wasm benchmark?