Make test-all.sh run unit tests in debug mode.

It turns out that "cargo test --release" doesn't use
`[profile.release]`; it uses `[profile.bench]` instead; see
[here](https://doc.rust-lang.org/cargo/reference/manifest.html) for details.
So the plan to run the tests in optimized mode but with debug-assertions
enabled didn't actually work, and we had an actual failing unit test that
was hidden because assertions were disabled.

So, this makes test-all.sh just run the unit tests in debug mode, as is
the norm for Rust packages, and fixes the buggy test.

This also removes the `[profile.release]` override from the top-level
Cargo.toml file too. We don't need it now that we're not running tests
in release mode, and it had confused multiple people because it made
Cretonne's in-tree builds different from how Cretonne is built when used as
a dependency in other projects.

cranelift/Cargo.toml

@@ -31,11 +31,3 @@ tempdir = "0.3.5"
 term = "0.5.1"
 
 [workspace]
-
-# Enable debug assertions and parallel compilation when building cretonne-tools
-# since they are for testing and development mostly. This doesn't affect the
-# flags used to build the cretonne-* crates when used as a dependency.
-[profile.release]
-opt-level = 2
-debug-assertions = true
-codegen-units = 4