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/llvm_arguments.rs

@@ -0,0 +1,15 @@
+use crate::tests::cli::utils::{
+    assert_command_success, execute_resolc, RESOLC_YUL_FLAG, YUL_CONTRACT_PATH,
+};
+
+#[test]
+fn llvm_arguments_work_with_yul_input() {
+    let output_with_argument = execute_resolc(&[
+        RESOLC_YUL_FLAG,
+        YUL_CONTRACT_PATH,
+        "--llvm-arg=-riscv-soften-spills'",
+        "--bin",
+    ]);
+    assert_command_success(&output_with_argument, "Providing LLVM arguments");
+    assert!(output_with_argument.success);
+}