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/llvm-context/src/polkavm/context/function/runtime/deploy_code.rs

@@ -1,47 +1,36 @@
 //! The deploy code function.
 
-use std::marker::PhantomData;
-
 use crate::polkavm::context::code_type::CodeType;
 use crate::polkavm::context::function::runtime;
 use crate::polkavm::context::Context;
-use crate::polkavm::Dependency;
 use crate::polkavm::WriteLLVM;
 
 /// The deploy code function.
 /// Is a special function that is only used by the front-end generated code.
 #[derive(Debug)]
-pub struct DeployCode<B, D>
+pub struct DeployCode<B>
 where
-    B: WriteLLVM<D>,
-    D: Dependency + Clone,
+    B: WriteLLVM,
 {
     /// The deploy code AST representation.
     inner: B,
-    /// The `D` phantom data.
-    _pd: PhantomData<D>,
 }
 
-impl<B, D> DeployCode<B, D>
+impl<B> DeployCode<B>
 where
-    B: WriteLLVM<D>,
-    D: Dependency + Clone,
+    B: WriteLLVM,
 {
     /// A shortcut constructor.
     pub fn new(inner: B) -> Self {
-        Self {
-            inner,
-            _pd: PhantomData,
-        }
+        Self { inner }
     }
 }
 
-impl<B, D> WriteLLVM<D> for DeployCode<B, D>
+impl<B> WriteLLVM for DeployCode<B>
 where
-    B: WriteLLVM<D>,
-    D: Dependency + Clone,
+    B: WriteLLVM,
 {
-    fn declare(&mut self, context: &mut Context<D>) -> anyhow::Result<()> {
+    fn declare(&mut self, context: &mut Context) -> anyhow::Result<()> {
         let function_type = context.function_type::<inkwell::types::BasicTypeEnum>(vec![], 0);
         context.add_function(
             runtime::FUNCTION_DEPLOY_CODE,
@@ -54,7 +43,7 @@ where
         self.inner.declare(context)
     }
 
-    fn into_llvm(self, context: &mut Context<D>) -> anyhow::Result<()> {
+    fn into_llvm(self, context: &mut Context) -> anyhow::Result<()> {
         context.set_current_function(runtime::FUNCTION_DEPLOY_CODE, None)?;
 
         context.set_basic_block(context.current_function().borrow().entry_block());