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/common/src/object.rs

@@ -0,0 +1,61 @@
+//! The revive binary object helper module.
+
+use std::str::FromStr;
+
+use serde::{Deserialize, Serialize};
+
+/// The binary object format.
+///
+/// Unlinked contracts are stored in a different object format
+/// than final (linked) contract blobs.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub enum ObjectFormat {
+    /// The unlinked ELF object format.
+    ELF,
+    /// The fully linked PVM format.
+    PVM,
+}
+
+impl ObjectFormat {
+    pub const PVM_MAGIC: [u8; 4] = [b'P', b'V', b'M', b'\0'];
+    pub const ELF_MAGIC: [u8; 4] = [0x7f, b'E', b'L', b'F'];
+}
+
+impl FromStr for ObjectFormat {
+    type Err = anyhow::Error;
+
+    fn from_str(value: &str) -> Result<Self, Self::Err> {
+        match value {
+            "ELF" => Ok(Self::ELF),
+            "PVM" => Ok(Self::PVM),
+            _ => anyhow::bail!(
+                "Unknown object format: {value}. Supported formats: {}, {}",
+                Self::ELF.to_string(),
+                Self::PVM.to_string()
+            ),
+        }
+    }
+}
+
+impl TryFrom<&[u8]> for ObjectFormat {
+    type Error = &'static str;
+
+    fn try_from(value: &[u8]) -> Result<Self, Self::Error> {
+        if value.starts_with(&Self::PVM_MAGIC) {
+            return Ok(Self::PVM);
+        }
+        if value.starts_with(&Self::ELF_MAGIC) {
+            return Ok(Self::ELF);
+        }
+        Err("expected a contract object")
+    }
+}
+
+impl std::fmt::Display for ObjectFormat {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::ELF => write!(f, "ELF"),
+            Self::PVM => write!(f, "PVM"),
+        }
+    }
+}