Separate compilation and linker phases (#376)

Separate between compilation and linker phases to allow deploy time
linking and back-porting era compiler changes to fix #91. Unlinked
contract binaries (caused by missing libraries or missing factory
dependencies in turn) are emitted as raw ELF object.

Few drive by fixes:
- #98
- A compiler panic on missing libraries definitions.
- Fixes some incosistent type forwarding in JSON output (empty string
vs. null object).
- Remove the unused fallback for size optimization setting.
- Remove the broken `--lvm-ir`  mode.
- CI workflow fixes.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>
Signed-off-by: xermicus <bigcyrill@hotmail.com>
Signed-off-by: xermicus <cyrill@parity.io>

crates/common/src/keccak256.rs

@@ -0,0 +1,68 @@
+//! Keccak-256 hash utilities.
+
+use serde::{Deserialize, Serialize};
+use sha3::digest::FixedOutput;
+use sha3::Digest;
+
+pub const DIGEST_BYTES: usize = 32;
+
+/// Keccak-256 hash utilities.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub struct Keccak256 {
+    /// Binary representation.
+    bytes: [u8; DIGEST_BYTES],
+    /// Hexadecimal string representation.
+    string: String,
+}
+
+impl Keccak256 {
+    /// Computes the `keccak256` hash for `preimage`.
+    pub fn from_slice(preimage: &[u8]) -> Self {
+        let bytes = sha3::Keccak256::digest(preimage).into();
+        let string = format!("0x{}", hex::encode(bytes));
+        Self { bytes, string }
+    }
+
+    /// Computes the `keccak256` hash for an array of `preimages`.
+    pub fn from_slices<R: AsRef<[u8]>>(preimages: &[R]) -> Self {
+        let mut hasher = sha3::Keccak256::new();
+        for preimage in preimages.iter() {
+            hasher.update(preimage);
+        }
+        let bytes: [u8; DIGEST_BYTES] = hasher.finalize_fixed().into();
+        let string = format!("0x{}", hex::encode(bytes));
+        Self { bytes, string }
+    }
+
+    /// Returns a reference to the 32-byte SHA-3 hash.
+    pub fn as_bytes(&self) -> &[u8] {
+        self.bytes.as_slice()
+    }
+
+    /// Returns a reference to the hexadecimal string representation.
+    pub fn as_str(&self) -> &str {
+        self.string.as_str()
+    }
+
+    /// Extracts the binary representation.
+    pub fn to_vec(&self) -> Vec<u8> {
+        self.bytes.to_vec()
+    }
+}
+
+impl std::fmt::Display for Keccak256 {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "{}", self.as_str())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn hash_and_stringify_works() {
+        assert_eq!(
+            super::Keccak256::from_slices(&["foo".as_bytes(), "bar".as_bytes(),]).as_str(),
+            "0x38d18acb67d25c8bb9942764b62f18e17054f66a817bd4295423adf9ed98873e"
+        );
+    }
+}