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/resolc/src/tests/unit/remappings.rs

@@ -0,0 +1,40 @@
+//! The Solidity compiler unit tests for remappings.
+
+use crate::test_utils::{build_solidity_with_options, sources};
+
+#[test]
+fn default() {
+    let callee_code = r#"
+// SPDX-License-Identifier: MIT
+
+pragma solidity >=0.4.16;
+
+contract Callable {
+    function f(uint a) public pure returns(uint) {
+        return a * 2;
+    }
+}"#;
+
+    let caller_code = r#"
+// SPDX-License-Identifier: MIT
+
+pragma solidity >=0.4.16;
+
+import "libraries/default/callable.sol";
+
+contract Main {
+    function main(Callable callable) public returns(uint) {
+        return callable.f(5);
+    }
+}"#;
+
+    build_solidity_with_options(
+        sources(&[("./test.sol", caller_code), ("./callable.sol", callee_code)]),
+        Default::default(),
+        ["libraries/default/=./".to_owned()].into(),
+        revive_llvm_context::OptimizerSettings::cycles(),
+        true,
+        Default::default(),
+    )
+    .unwrap();
+}