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/global.rs

@@ -5,7 +5,6 @@ use inkwell::values::BasicValue;
 
 use crate::polkavm::context::address_space::AddressSpace;
 use crate::polkavm::context::Context;
-use crate::PolkaVMDependency;
 
 /// The LLVM global value.
 #[derive(Debug, Clone, Copy)]
@@ -18,15 +17,14 @@ pub struct Global<'ctx> {
 
 impl<'ctx> Global<'ctx> {
     /// A shortcut constructor.
-    pub fn new<D, T, V>(
-        context: &mut Context<'ctx, D>,
+    pub fn new<T, V>(
+        context: &mut Context<'ctx>,
         r#type: T,
         address_space: AddressSpace,
         initializer: V,
         name: &str,
     ) -> Self
     where
-        D: PolkaVMDependency + Clone,
         T: BasicType<'ctx>,
         V: BasicValue<'ctx>,
     {
@@ -53,14 +51,13 @@ impl<'ctx> Global<'ctx> {
     }
 
     /// Construct an external global.
-    pub fn declare<D, T>(
-        context: &mut Context<'ctx, D>,
+    pub fn declare<T>(
+        context: &mut Context<'ctx>,
         r#type: T,
         address_space: AddressSpace,
         name: &str,
     ) -> Self
     where
-        D: PolkaVMDependency + Clone,
         T: BasicType<'ctx>,
     {
         let r#type = r#type.as_basic_type_enum();