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/asm.rs

@@ -1,7 +1,5 @@
 //! The tests for running resolc with asm option.
 
-#![cfg(test)]
-
 use crate::tests::cli::utils;
 
 const ASM_OPTION: &str = "--asm";
@@ -30,10 +28,7 @@ fn fails_without_input_file() {
     utils::assert_command_failure(&resolc_result, "Omitting an input file");
 
     let output = resolc_result.stderr.to_lowercase();
-    assert!(
-        output.contains("no input sources specified") || output.contains("compilation aborted"),
-        "Expected the output to contain a specific error message."
-    );
+    assert!(output.contains("no input sources specified"));
 
     let solc_result = utils::execute_solc(arguments);
     utils::assert_equal_exit_codes(&solc_result, &resolc_result);