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/cli/usage.rs

@@ -1,20 +1,14 @@
 //! The tests for running resolc when expecting usage output.
 
-#![cfg(test)]
-
 use crate::tests::cli::utils;
 
 #[test]
-#[ignore = "Fix: 'resolc --help' should exit with success exit code"]
 fn shows_usage_with_help() {
     let arguments = &["--help"];
     let resolc_result = utils::execute_resolc(arguments);
     utils::assert_command_success(&resolc_result, "Providing the `--help` option");
 
-    assert!(
-        resolc_result.stdout.contains("Usage: resolc"),
-        "Expected the output to contain usage information."
-    );
+    assert!(resolc_result.stdout.contains("Usage: resolc"));
 
     let solc_result = utils::execute_solc(arguments);
     utils::assert_equal_exit_codes(&solc_result, &resolc_result);
@@ -25,10 +19,7 @@ fn fails_without_options() {
     let resolc_result = utils::execute_resolc(&[]);
     utils::assert_command_failure(&resolc_result, "Omitting options");
 
-    assert!(
-        resolc_result.stderr.contains("Usage: resolc"),
-        "Expected the output to contain usage information."
-    );
+    assert!(resolc_result.stderr.contains("Usage: resolc"));
 
     let solc_result = utils::execute_solc(&[]);
     utils::assert_equal_exit_codes(&solc_result, &resolc_result);